Site Study Descriptions
Site Selection
Three sites — Fairfax County, Virginia; the City of Plano, Texas; and the City of St. Paul, Minnesota — are featured in this section. They represent a range of system maturity, stakeholder relationships, signal operating concepts, and deployment and operational approaches.
As of 2004, Fairfax County was in the process of equipping selected corridors within a large, highly integrated regional traffic signal system. Plano, Texas has a 20-year history of operating EVP across 100 percent of its signals, which were equipped incrementally as part of a comprehensive growth plan. St. Paul has over 25 years of operating experience across 100 percent of its signals, which were equipped retroactively as part of a multi-year EVP deployment plan. Table 5 provides a snapshot of key characteristics of each site.
| Site Characteristics | Fairfax County, VA | Plano, TX | St. Paul, MN |
|---|---|---|---|
| Area (Mi2) | 497 | 76 | 53 |
| Equipped Signals/Total Signals | 37/1,034* | 194/194 | 368/368 |
| Signal Controller Type | Type 170 | Type 170† | Type 170 |
| Central Signal Control Center | Yes | Yes | Yes |
| Signal Operations Mode | Semi-actuated | Semi-actuated | Semi-actuated |
| Communication with Signals | Twisted copper phone lines | Wireless | Twisted copper phone lines |
| Preemption Technology Employed | Vehicle-based light emitter | Vehicle-based light emitter | Vehicle-based light emitter |
| EV Classes Served | Fire/rescue and EMS | Fire/rescue and EMS | Fire/rescue, EMS, and police |
| Transit Priority | Yes | No | No |
| * The signals in Fairfax County are part of
the Virginia Department of Transportation (VDOT) Smart Traffic Signal
System that is a highly integrated system operating across three Northern
Virginia counties. † The City of Plano, Texas operated Type 170 controllers at the time that interviews and site visits were conducted for this study. However, the City upgraded to Type 2070 controllers in 2004. |
|||
This section presents each site's EVP deployment and operations experience in terms of the history of the deployment, the site's traffic operations conditions, the emergency services operational environment, and the operation and maintenance concepts.
Fairfax County, Virginia
Fairfax County is one of four counties that make up the Northern Virginia region. The county covers an area of 407 square miles with a population of approximately one million.17 The county seat is located approximately 12 miles southwest of Washington, D.C. Development in the county is diverse, ranging from high density office complexes, technology campuses, and commercial development to residential areas that range from medium rise apartments and town homes to single family homes in neighborhoods and rural acreage settings.
EVP Deployment History
Fairfax County has been a leader in the regional push for EVP that first started in the mid-1980s. During this period, fire/rescue and EMS chiefs across Northern Virginia's four counties identified EVP as a means to offset the negative impact that growing congestion was having on EV response times and on EV crash potential. Since the concept was first introduced, EVP in Fairfax County has been deployed in several distinct phases. In the first phase, the county installed EVP on signals that provide arterial access from off-street stations. The second phase consisted of installation of EVP on problem intersections on a case-by-case basis. The third phase consisted of installation of EVP on a small number of intersections located downstream from arterial access points equipped in the first phase (typically one or two intersections). Success in these deployments led to a larger initiative to expand EVP to support EV operations on a corridor level.
|
"With the extremely high number of emergency calls for the U.S. 1 fire and rescue stations, not to mention the heavy traffic volumes in the background, the corridor was the perfect candidate for emergency vehicle signal preemption." — Doug Hansen Senior Transportation Planner Fairfax County |
The proposal to equip arterial signals on a corridor basis emerged in 1997. The initiative did not progress initially because of concerns over the impact on the operation and performance of the Northern Virginia Smart Traffic Signal System, operated by the Virginia Department of Transportation (VDOT). The corridors proposed by fire/rescue and EMS officials were all high interest corridors from a traffic signal system operation perspective, as they operate at near saturation conditions during much of the day. The initiative stalled until the system champions decided to raise the issue on a regional level within the signal operations committee of the Washington D.C. Council of Governments. This action increased the supportive stakeholder base as county transportation officials became interested in the concept as a way to support development of advanced public transportation corridors equipped to provide transit signal priority.
With a broader stakeholder base and increased momentum, VDOT proposed a test plan that involved various technologies and operational concepts. Fairfax County was selected by the U.S. DOT for a test of integrated EVP and transit signal priority using optical emitter and detection systems. The test was conducted on a section of U.S. 1 located just south of Alexandria, Virginia.
The test section was a 1.3-mile stretch of roadway that operated under heavy traffic load during rush hours. The section had seven signals operating on six Type 170 controllers. At the mid-point of the test section, a minor side street intersection provided arterial access for Fire and Rescue Station 11, which was the busiest station in the county.
|
"Our goal with the EVP program is to get our fire and rescue personnel onto the roadway safely and to get them to the scene as quickly and safely as possible." — Eddie Beitzel
Fire and Rescue Department Planner Fairfax County |
Transit operations on the test section included five fixed-schedule routes. The local Fairfax Connector operated three of these and the Washington Metropolitan Area Transit Authority (WMATA) operated two. During the peak periods, between the two services, buses ran at 10-minute headways through this important transit corridor that serves both point-to-point riders as well as those traveling by bus to transfer to the WMATA operated subway.
In late 2003, the field test results were reviewed. Measures of benefit and impact indicated that EVP and transit signal priority could be operated on the busy U.S. 1 corridor. As a result of this report, VDOT authorized Fairfax County to progress with the installation of EVP and transit signal priority on all signals on the 13-mile portion of U.S. 1 that falls within the county. The installation of the newly approved signals was completed in 2004.
Traffic Operations on U.S. 1
The signals on U.S. 1 in Fairfax County are owned and operated by VDOT and they are operated as part of a network of over 1,000 signals serving Northern Virginia. During most of the day, the signals operate in the semi-actuated mode with offsets programmed to support progression in peak directions. Rush hour cycle times are typically 180 seconds. At the major intersections, the green time split approaches 67 percent on the arterial and 33 percent on the side streets. During the morning peak period, queues on the arterial approaches to major intersections on U.S. 1 typically will be between 12 and 18 vehicles deep across all three travel lanes and the left turn pockets will be full at intersections with major side-streets.
Emergency Service Operations
EV trip generation in Fairfax County is significant with 90,000 emergency response calls per year. These responses originate from 35 stations that house both fire/rescue and EMS units. The response time goal for the county is 5 minutes from the time of dispatch for fire suppression and 6 minutes from the time of dispatch for the arrival of advanced life support. These goals were set based on National Fire Protection Association (NFPA) flashover curves and American Heart Association criteria for responses to cardiac arrest. Fire/rescue and EMS performance against these and other goals is reported to the county Board of Supervisors annually.
At present, the county operates 35 fire/rescue and EMS stations. Each station is responsible for approximately 11.5 square miles. Each station is staffed full time by career fire/rescue and EMS personnel, although 11 of the stations also have volunteers. The county's long-range fire/rescue and emergency medical service plan calls for 40 stations when the county completes development according to its comprehensive plan. One of the key assumptions in the planning methodology includes maintaining an average EV speed of 32.6 mph. Fire/rescue and emergency medical service performance is periodically reviewed as part of the county's long range planning effort. These reviews have highlighted three corridors, including U.S. 1, for which the county plans to pursue corridor level deployment to offset reductions in average EV speeds caused by congestion.
Fairfax County, Virginia, EVP System Highlights:
|
In Fairfax, only fire/rescue and EMS vehicles have access to the full EVP system. However, transit services operating on the corridor include approximately six buses per hour during the AM and PM peak periods that are equipped with the optical emitters. However, transit vehicle emitters operate on the low priority setting which activates transit priority based on satisfaction of preset conditions, one of which is to yield to any EVP request.
Preemption in Fairfax County is provided only on the arterial approaches because the EV trip patterns generally include a segment of arterial travel followed by turnoff on to collector roads, and then turns on to neighborhood or commercial area streets. The detectors are set to support a detection range of approximately 1,600 feet except in cases of closely spaced intersections or where roadside features cause problems with preemption activation. The goal is to disperse the queues to the point where the private vehicle drivers can move into the middle and right lanes allowing the EV to maintain speed in the left. For preemption, the only condition for request approval is that the signal is not in a pedestrian phase. All other times, the controller will reference the transition plan and move from the current phase while honoring minimum green and amber times.
Once in preemption, the signal displays a green ball or green arrow on all signal heads on the EV arterial approach. All movements on all other approaches are brought to a red interval. This phase design is consistent with displays that drivers normally see on the arterial under normal semi-actuated operating conditions.
Plano, Texas
Plano, Texas, is a suburb located approximately 20 miles northeast of Dallas. Plano is an incorporated city with a population of approximately 220,000.18 As of 2004, the city size was 74 square miles, although the city experiences a slow but steady growth due to annexation. Within the city, land use varies from moderate density residential to commercial campus development. Light commercial and retail facilities complement the surrounding residential and commercial campus areas. The downtown area consists of approximately 16 square blocks made up of multistory residential apartments, street front stores, and restaurants, as well as private and public office buildings.
EVP Deployment History
EVP deployment began in 1984 as the result of an initiative by the fire chief. The chief had moved to Plano in 1982 from a jurisdiction in Illinois where he led an effort to equip a small corridor with EVP equipment to reduce EV crashes. In Plano, the chief wanted to address a high EV crash rate. Analysis of the EV crash history for the preceding three-year period indicated that nearly 1/3 of the 22 total EV crashes occurred at signalized intersections.
In the early 1980s, Plano had a population of approximately 50,000 and covered approximately 16 square miles. However, growth forecasts and the city's master development plan estimated that in the next 20 years, the population would reach 250,000 and cover approximately 75 to 80 square miles. Keeping this forecast in mind, the fire chief encouraged a capital improvement bond that could serve as a funding mechanism. To develop support, the fire chief worked with a citizens' advisory committee to develop a fire protection master plan. The advisory committee and the chief proposed the retrofit of all existing signals and the inclusion of EVP for all new signals.
The initial deployment to retrofit 46 intersections took three years, resulting in a 100 percent deployment by 1987. As the city grew, 10 to 17 new signals were installed each year. Each new signal was designed, priced, and installed with integrated preemption equipment. Plano continues to have 100 percent preemption coverage.
Traffic Operations
Traffic patterns in Plano have grown more complex as peak periods have gotten longer over the past 10 years. Commute patterns have shifted from primarily morning and evening commutes to and from Dallas to more random patterns typical of widely distributed points of origin and destination. The transportation network is made up primarily of arterial roadways laid out in a grid system. The arterial roadways are all built in a boulevard fashion so opposing traffic is separated by treelined grass medians bordered by non-mountable curbs (Figure 6). Multilane queues of up to 22 vehicles long are typical.
Figure 6. Typical Intersection in Plano, Texas, During Morning Rush Hour
Plano owns and operates all 194 traffic signals in its system. Although Plano originally used Type 170 controllers at each signal, the city upgraded to Type 2070 controllers in 2004. The city runs a centralized traffic management and control center that communicates with signal controllers continuously via wireless transmission.
The traffic signal timing plan varies throughout the day. During the peak periods, the signals operate in the semi-actuated mode with offsets to optimize progression in the peak direction. During non-peak periods, the signals operate in a semi-actuated mode, free mode, or flashing mode, depending on the location and the time of day. Major intersections operate on 160-second cycles and, signals at the minor intersections operate on 80-second cycles. During the morning peak period, queues on all four approaches to major intersections will typically be between 18 and 22 vehicles deep with some cases exceeding 30 vehicles.
Emergency Service Operations
EV trip generation in Plano is relatively high with 16,000 emergency response calls per year from 10 fire/rescue and EMS stations. These responses generate an average of one preemption request per day per signal across the city. Some signals, located near hospitals and fire/rescue and EMS stations, are preempted as many as 15 times in a day or, on average, once every 90 minutes.
The response time goal for the city of Plano has been set at 90 percent of calls responded to within 6 minutes, 59 seconds. This goal was set by the City Council to affirm the city's commitment to responsive public safety services. As part of its continuing commitment, the fire chief delivers an annual summary presentation to the City Council that details the department's performance in the preceding year by zone within the city.
Zones in which the goal is not met are reviewed for potential policy or capitalization initiatives to improve the level of service. The city operates one fire station for every 7.5 square miles of incorporated area. Eight of the 10 stations operate at normal staffing and equipment levels. Two stations have additional personnel and equipment assigned to offset growth and congestion trends in one area of the city under consideration for a new station. It is expected that one more station will be built in the near term.
Preemption System Operations
In Plano, only fire/rescue and EMS vehicles have access to the EVP system. The system was a fire department initiative. Over the 20-year operational period, neither police nor transit officials have expressed strong interest in using the system.
Plano, Texas EVP System Highlights:
|
All compatible emitter-equipped vehicles from the surrounding communities are allowed to access the Plano system. Similarly, Plano's emergency vehicles are permitted access to the priority systems of their neighboring communities. As of 2004, Plano is considering moving toward encrypted system use due to the appearance on the retail market of devices that claim to activate EVP for ordinary auto drivers. Enhancing the system with encryption will require coordination with the surrounding communities. All Plano emitters are capable of encryption; however, not all intersections are equipped with detectors capable of operating in an encrypted mode. Encryption is expected to prevent unauthorized users from accessing the system in addition to providing a record of which EVs used the system and when.
Preemption in Plano is provided on all four approaches to each intersection. This configuration supports the EV trip patterns in which EVs can proceed to a destination using the grid-oriented arterial road system. The detectors are set to support a detection range of approximately 1,600 feet unless roadway or roadside features restrict ranges due to line-of-sight problems. The goal is to have a minimum span of 20 seconds between the call and the arrival of the emergency vehicle at the signal. For preemption, the only condition for request approval is that the signal is not in a pedestrian phase. All other times, the controller will transition from the current phase at the expiration of the minimum green time.
Once in preemption, the signal displays a green ball or green arrow on all signal heads on the EV approach. All movements on all other approaches will be brought to a red interval. This phase design is consistent to displays that are generated on the arterial under normal semi-actuated operating conditions.
St. Paul, Minnesota
The City of St. Paul is one of the two Twin Cities of Minnesota that form the heart of the largest metropolitan area in the state, with a total population of nearly 3 million people.19 St. Paul is an incorporated city, with a population of approximately 288,000 and a land area of 53 square miles. Within the city, land use varies from single-family neighborhoods, to moderate-density residential and commercial, to a high-density central business district. The downtown area of St. Paul consists of approximately 70 square blocks with a variety of multistory residential apartments, street front stores and restaurants, and high-rise office buildings, both privately and publicly owned.
EVP Deployment History
In 1969, EVP was implemented at 28 intersections in St. Paul as the first step in an effort to reduce the number of EV crashes experienced each year. Between 1969 and 1976, the city equipped 285 of its 308 intersections with optical EVP systems. Initially, the deployment was only on the two main approaches to each intersection. This deployment plan was modified in 1972 after a fatal crash occurred between a police car and a fire truck at an EVP-equipped intersection. After this incident, the mayor of St. Paul decided to provide full coverage of the preemption system to all intersections on all approaches. As of 2004, St. Paul operated an EVP system on 100 percent of its 368 traffic signals on all approaches. New traffic signals installed in St. Paul are outfitted with preemption equipment during construction.
Traffic Operations
The transportation network is comprised primarily of major and minor streets laid out in a grid system. A sub-grid of minor streets between the arterials provides access to various neighborhoods and commercial areas. Throughout the city, the streets are bounded on the right side by nonmountable curbs and sidewalks but most do not have raised center medians. As is the case with many central business districts throughout the country, the downtown area of St. Paul has short blocks and several one-way streets.
St. Paul owns and operates all of the traffic signals that serve the city. Each signal is controlled by Type 170 equipment from a centralized traffic management center by the Traffic Operations section of the City of St. Paul Department of Public Works. The Traffic Operations staff can monitor signal operations continuously and can send updated signal timings to intersections through a combination of broadband and twisted copper wire communication connections. Most signals in the city operate on a 60-second cycle length. Some of the more heavily traveled corridors have cycle lengths of 120 seconds. During the peak periods, the signals typically operate in the semi-actuated mode with offsets to optimize progression in the peak direction. During non-peak periods, the signals operate in a semi-actuated mode, a free mode, or in a flashing mode, depending on the location and the time of day.
Emergency Service Operation
St. Paul fire/rescue and EMS vehicles respond to approximately 26,000 emergency calls per year from 16 fire/rescue and EMS stations. Fire suppression responses account for approximately 12,500 of these calls; emergency medical services account for the remaining 13,500 calls, with an average of approximately 70 emergency response calls per day, or about one call every 20 minutes.
In contrast to Fairfax County and Plano, the City of St. Paul EVP system is used by the police department as well as fire/rescue and emergency medical services. The inclusion of police as system users places a significantly higher demand on the system. Police receive 263,000 calls annually, with an average of 720 calls per day or, one police response every 2 minutes. In addition to the increased demand, police use of the system differs from fire/rescue and EMS in trip origin and travel route patterns. While fire/rescue and emergency medical services primarily respond from fixed stations and travel along predictable routes, police vehicles respond from random locations and make route choices quickly as police officers select routes considering both tactical advantage and response urgency.
The combination of fire/rescue, EMS, and police use produces a less predictable preemption pattern, but there are still some areas of the city and some signals within the city where the average number of preemption events in a day is higher than others. Signals located near hospitals and fire/rescue and EMS stations are preempted more than five times per day while others are only preempted a few times per week. The response time goal for the fire department in St. Paul is 3 minutes for both fire/rescue and EMS responses. The police department does not specify a time goal because dispatchers contact officers in the field who respond from various locations to emergency calls.
Preemption System Operations
St. Paul is one of only a few jurisdictions in the country that provides preemption access to every police vehicle, as well as every fire and emergency vehicle, in the city. Additionally, all emitter-equipped vehicles from the surrounding communities are allowed to access the St. Paul system if they are willing to enter a formal agreement with the city. The main elements of this agreement state that outside emergency departments will consent to fully train their employees for use of the preemption equipment, and that they will use the system "as-is," waiving any future legal action against the City of St. Paul for any damages arising from use of the system. Similarly, St. Paul's emergency vehicles are permitted full access to the preemption systems of the neighboring communities, although no formal agreement is required in most adjacent jurisdictions.
Preemption System Operations
In Plano, only fire/rescue and EMS vehicles have access to the EVP system. The system was a fire department initiative. Over the 20-year operational period, neither police nor transit officials have expressed strong interest in using the system.
St. Paul, Minnesota EVP System Highlights:
|
In St. Paul, the detection thresholds are all set to the maximum range of approximately 2,300 feet with a 2-second dwell requirement for call acceptance. The policy was developed in 1998 after the city conducted a system performance test in an effort to ensure the maximum benefit to the entire user community. The range setting accommodates police vehicles, which accelerate quickly and often operate at higher speeds than fire/rescue and EMS vehicles. In addition to the benefit for the police community, maximum range detection thresholds compensate for variation in emitter intensity across St. Paul's several generations of emitter equipment and variation in detection range caused by differences in emitter installation height. The 2-second dwell requirement reduces the number of inadvertent preemptions triggered when preemption equipped vehicles make turns in areas with closely spaced parallel streets.
Once in preemption, the signal displays a green ball on all through lanes for both the concurrent and opposing approaches. Left turn arrows on signals on the concurrent and opposing approach display a red arrow to prevent a motorist from making a permissive left turn across the path of an oncoming EV. Perpendicular approaches are brought to a red interval for movement in all directions.
The confirmation light is an important system feature of the St. Paul EVP system. The lights provide feedback to the EV drivers. The lights indicate that a request has been received and provide information on the precedence level of the request in cases when a simultaneous or near-simultaneous preemption request is made on a perpendicular approach. The approach that will get the green is provided with a solid confirmation light while those that will have to yield the right of way are provided with a flashing confirmation light. Operation of the confirmation light is part of EV driver training and is integral to the effort to reduce the potential for crashes.
Figure 7 shows a St. Paul traffic signal in the preemption phase with an EV crossing right to left through the intersection.
Figure 7. A St. Paul Signal in the Preemption Phase
17 U.S. Census Bureau Website (2004). http://www.census.gov.
18 Ibid.
19 Ibid.