New traffic control for an old pedestrian crossing safety problem
Richard B. Nassi, P.E., Ph.D., Transportation Administrator, City of Tucson, Arizona, and Michael J. Barton, P.E., PTOE, Transportation Business Group Manager, HDR Engineering, Tucson, Arizona
The development of uniform and effective pedestrian crossing treatments has been a constant challenge for traffic engineers over the past few decades and still is an issue today. Often, the techniques available didn't have a high rate of compliance and the lack of uniform standards have left local traffic engineers to experiment with a variety of crossing treatments to meet needs of pedestrians.
The Institute of Transportation Engineers (ITE) has addressed these issues of uniformity and compliance for pedestrian crossings numerous times over the past 40 years. In fact, Herman Bates noted in the June 1965 issue of Traffic Engineering that "...The lack of a generally accepted standard, designed to fit this problem (pedestrian crossings), has left a vacuum which can only result in the continued use of non-uniform traffic control devices."
Jim Sparks, in the January 1990 issue of ITE Journal, expressed the following: "In summary, national literature and local experience in Phoenix, Arizona, show that flashers offer no benefit for intermittent pedestrian crossings in an urban environment. In addition, the longer the flasher operates, the more it becomes part of the scenery and eventually loses any effectiveness."
Even recently, Andrew Cooley, in the December 2006 issue of ITE Journal, says: "One of the challenges faced by engineers working on pedestrian improvements is the status of (conflicting) research and the absence of clear guidance."
The City of Tucson has wrestled with pedestrian crossing issues, particularly how to provide pedestrian crossings of major arterials at minor street intersections. This lead to the development of the High intensity Activated crossWalK (HAWK) Pedestrian Crossing Beacon Signal.
|The HAWK Crossing|
The HAWK Crossing is one of the newest crossing systems in use. It's based on a European signal design and is similar to the current American school bus warning flasher system. The HAWK consists of a standard traffic signal RED-RED over YELLOW format. The unit is dark until activated by a pedestrian. When pedestrians wish to cross the street, they press a button which activates a warning FLASHING YELLOW light on the main street. The indication then changes to a SOLID YELLOW advising drivers to prepare to stop. The signal then displays a DUAL SOLID RED and shows the pedestrian a WALK symbol. The beacon then displays an ALTERNATING FLASHING RED and the pedestrian is shown a FLASHING DON'T WALK with a "countdown" signal advising them of the time left to cross. Drivers are allowed to proceed during the flashing red after coming to a full stop and making sure there is no danger to a pedestrian.
This flashing operation allows the delay to the traffic to match the actual crossing needs of the pedestrian. If the pedestrian needs more time, then the drivers must remain stopped for the pedestrian. The need to balance the needs of the pedestrian and the drivers' delay is critical for the high compliance rates for the HAWK crossings. Currently, the operation has a 97 percent compliance rate. The driver will stop for the pedestrian and remain stopped as long as the reason for the stop is apparent. Extensive RED time, when the pedestrian no longer needs it to cross safely, will only encourage violations.
|Innovative Crosswalk Treatments|
In experimental use in Tucson the HAWK Pedestrian Crossing Beacon Signal was achieving very high compliance rates, which was documented most notably in the joint Transit Cooperative Research Program (TCRP) and the National Cooperative Highway Research Program (NCHRP) study entitled Improving Pedestrian Safety at Unsignalized Roadway Crossings. This study was intended to recommend engineering techniques to improve pedestrian safety at crossings of heavily-traveled roadways at unsignalized intersections, particularly those served by public transportation. Another goal of the study was to develop modifications to the Manual on Uniform Traffic Control Devices (MUTCD) pedestrian traffic signal warrant.
The study reviewed a variety of crossing methods and measured driver compliance to the use of various traffic control devices. The chart at left shows the results of the TCRP/NCHRP compliance study (numbers show percent compliance).
The results of the compliance were so favorable that one of the major recommendations resulting from the study was the following:
RED SIGNAL OR BEACON DEVICES need to be added to the engineer's toolbox for pedestrian crossings. The study results indicated that all red signal or beacon devices were effective at prompting high levels of motorist yielding on busy arterial streets. However, only a midblock traffic signal is currently recognized in the MUTCD, and the current pedestrian signal warrant is very difficult to meet. Thus, in the current situation, engineers are unable to employ those traffic control devices that are most effective for pedestrians on wide arterial streets.
The study also recommended that such devices be included in the MUTCD. The researchers worked with the members of the National Committee of Uniform Traffic Control Devices (NCUTCD), Signal Technical Committee (STC), to develop suitable language for the inclusion of HAWK Pedestrian Beacon Signals in the MUTCD.
The researchers and NCUTCD, STC developed draft language that went out for technical review and received a number of comments.
Issues with the HAWK
Although operational experience was favorable, four issues were identified that needed to be resolved before the HAWK Crossing Beacon Signal could be included in the MUTCD.
The comments fell into the following four categories.
The following sections of this article discuss how these concerns were handled, present crash information and discuss the future evolution of the device.
Dark Beacons. The first issue related to the operation of the device resting in the Dark Mode. As stipulated in the Uniform Vehicle Code, vehicles are required to stop at dark traffic signals and there was some concern that the HAWK device could be perceived as a non-operating traffic signal and cause drivers to stop unnecessarily.
|The Beacon Head configuration|
During the TCHRP/NCHRP research, the study (UNC PED) and local observation and operational experience did not observe this behavior. This is in part based on the Beacon Head configuration, which was modeled after similar devices used in Europe for decades. The signal lens configuration is modified from the Table 4D-3e.
Additionally, concerns were expressed that the HAWK could be considered a half signal, which is prohibited by the MUTCD. Unlike a half signal, where the signal indication for the main street rests in green with STOP signs on the side street, the HAWK's beacon operational sequence does not show conflicting information to drivers.
Potential Driver Confusion. In fact, a review of other approved pedestrian crossing techniques allowed by the MUTCD shows that the right-of-way rules remain unchanged.
|Normal Crosswalk (driver compliance: 17-20%)|
For a normal crosswalk the following is required:
Additionally, based on the TCRP/NCHRP, the driver compliance for this crossing technique is 17 to 20 percent.
|In-Roadway Flashers (driver compliance: 66%)|
For a location with in-roadway flashers, the following is required:
Additionally, based on the TCRP/NCHRP, the driver compliance for this crossing technique was an average of 66 percent. The TCRP/NCHRP report actually reviewed numerous studies and found compliance rates ranged from 8 to 100%.
|Flashing Beacon (driver compliance: 47-49%)|
For a location with a flashing beacon, the following is required:
Additionally, based on the TCRP/NCHRP, the driver compliance for this crossing technique is 47 to 49 percent.
|HAWK Pedestrian Beacon (driver compliance: 97%)|
For a location with a HAWK Pedestrian Crossing Beacon Signal, the following is required:
Additionally, based on the TCRP/NCHRP, the driver compliance for this crossing technique is 97 percent.
As noted in the above discussion, the drivers' responsibilities do not change for any of the traffic control situations. Drivers facing the stop sign are not given the right-of-way to cross the street over main street traffic. The HAWK pedestrian beacon is basically a supplement to the current right-of-way codes.
Proliferation of Devices. Another concern was the potential for the proliferation of devices. In order to address this concern, the authors of the TCRP/NCHRP in conjunction with the NUCTD, STC worked to develop some proposed guidelines, based on research that would provide practitioners guidance on when the installation HAWK Crossing Beacon Signal should be considered.
Typically beacon devices do not have numeric warrants or guidelines, but due to the uniqueness of this device more guidance was deemed necessary.
Tucson has encountered many situations where there has been a need for a device at crosswalks that is more than a flashing beacon, but where a full signal is not warranted or appropriate. The HAWK is such a device. Often it has been utilized in lieu of a full traffic signal and to replace a flashing beacon with low compliance rates. Therefore, it is often not adding devices, it is replacing devices with a more appropriate treatment.
Tucson's experience has been when full signals are utilized at minor cross streets, for other pedestrian needs, the minor streets tend to attract additional traffic making them "de facto arterials." This is oftentimes at odds with neighborhoods or other stakeholders.
Because the HAWK operates as a beacon and is only activated when needed, the device limits impacts to arterial progression that would be created by a full traffic signal installation. Additionally, the HAWK can also be run at half cycles with the full arterial progression which also limits impacts. The use of the flashing red also reduces delay by allowing vehicles to proceed, after making a stop, once a pedestrian has cleared the crosswalk.
Uniformity. Finally, there was some concern regarding uniformity. In reviewing current practice across the country, a variety of treatments was observed. This was the main reason why there was a concerted effort to develop language to include this device in the MUTCD. As indicated previously, current traffic control standards have proven inadequate to meet the pedestrian needs and because of that, numerous non-uniform designs have proliferated with varying levels of success. The HAWK Pedestrian Beacon will provide a uniform device with extremely high driver compliance to accommodate many applications.
The City of Tucson has installed over 60 HAWK Crossing Beacon Signals and has not experienced a high occurrence of crashes at these locations and has had no pedestrian fatalities at any of the locations. In fact, during the last five years there have only been nine pedestrian accidents at these locations. The breakdown is as follows:
Therefore, city-wide HAWK pedestrian beacons for over 60 locations average approximately 1.8 crashes per year. It is critical to note that there are times when pedestrians do not activate the HAWK beacons when crossing. If you remove those pedestrian crashes, when the lights were not activated, the average annual pedestrian crashes drops to approximately 1.3 crashes per year. These are extremely low crash rates considering the number of crossings in operation and that these averages are far below the pedestrian crash experience that can be observed at full traffic signals. The success of the HAWK implementations has also received favorable treatment from the local media.
Tucson follow-up study
During the development of language for the MUTCD the City of Tucson reviewed two specific HAWK locations to provide a better understanding of accident patterns and driver compliance.
The first location was at Irvington Road and 9th Avenue. This location was reviewed for the years 2002-2005 and had a total of 24 accidents, and only one of those involved a pedestrian. That particular accident occurred at an unmarked crossing opposite the marked crosswalk associated with the HAWK Pedestrian Beacon. The HAWK was not activated when this accident occurred. This location is at an arterial roadway (Irvington Road with 32,800 vehicles per day) with a minor side street (9th Avenue with less than 1,000 vehicles per day) intersection. This location is also adjacent to a major transit facility that has over 20 bus arrivals and departures every hour.
The second location was at Speedway Boulevard and Plumer Avenue. This location was reviewed for the years 2003-2006 and had a total of 15 accidents and none involving a pedestrian. This location is at an arterial roadway (Speedway Boulevard with 55,900 vehicles per day) with a minor side street (Plumer Avenue with less than 1,000 vehicles per day) intersection.
The review of these two locations indicates a low frequency of crashes compared with intersections with traffic signals. It is also critical to note that side street traffic has not been found to be involved at a significant level with crashes at these minor street intersections with HAWK Pedestrian Beacons. In fact, at the locations reviewed, the side street accident occurred when the HAWK Pedestrian Beacon was not activated. Additionally, rear end accidents were the predominant accident type, which is typical of locations with STOP control of some fashion. Even though flashing yellow indications are provided before a solid yellow clearance interval, some drivers experience difficulty with stop control.
Currently, the Federal Highway Administration is considering decreasing the standard walking speed of 4 feet per second to 3.5 feet per second, which will have an effect on the timing of pedestrian signal intervals. The City of Tucson is experimenting with modified HAWK Pedestrian Crossing Beacon Signals that detect pedestrian walking speeds and will allow for extended signal phases as needed. The modified device is referred to as the PUFFIN (Pedestrian User Friendly INtersection).
The PUFFIN crossing is an extension of the HAWK operation that extends the pedestrian clearance beyond the normal settings when needed. The key to a successful crossing signaling operation is when the delay to the driver matches the needs of the pedestrian. Unnecessary delay will only encourage driver violations, just as extensive pedestrian delays will cause pedestrian violations. Of course, everyone should obey the signals, but they frequently do not. Thus, the need to balance the delays to a reasonable level is critical. This operation tries to manage the signal activation to be as near as possible to the "HOT" button response, giving a WALK signal as quickly as reasonably possible. The limits of the "HOT" operation are applied in a background cycle during the peak travel times. The pedestrian clearances are still set at 4 feet per second, but the side street timer of the controller is managed by a pedestrian detection device that can monitor the pedestrian's travel through the crosswalk. If the pedestrian needs more time, the controller provides a side street extension to the clearance interval, forcing a longer red to the drivers until an upper limit is reached. The upper side street extension is calculated using a pedestrian crossing speed of 3 feet per second from curb to curb or point of safe haven. The critical issue is that the pedestrian gets the time necessary to cross and the drivers are only delayed for the time the pedestrian really needs to cross. Nothing is worse for signal compliance levels than when the pedestrian has completed the crossing, but the signal is still showing the RED indication.
There have been no fatalities in any HAWK crossing to date (4/9/08). Accidents can happen at any time and engineering countermeasures can only do so much. The critical issue is that everyone needs to do their part and pay attention while crossing. The HAWK is another tool in the safety toolbox to assist the community.
"Engineering countermeasures can only go so far if you have people engaging in activities that put (their) lives at risk. Convincing people to change their behavior will have the most lasting effects; however this (goal) may be the most difficult thing to do in order to ensure pedestrian safety." - Tamara Redmon, "Fixing America's Pedestrian Safety Problem," TM+E Magazine, June/July 2003
The authors would like to acknowledge the tremendous assistance and guidance provided by the NCUTCD Signals Technical Committee and the authors of the TCRP/NCHRP research study, in particular Kay Fitzpatrick, P.E., Ph.D., of the Texas Transportation Institute.
Richard B. Nassi, P.E., Ph.D., is the Transportation Administrator for the City of Tucson and has more than 35 years of experience in the field. He is a registered Traffic Engineer in the State of California. He is a member of the National Committee on Uniform Traffic Control Devices, Signals Technical Committee. He is a Fellow of the Institute of Transportation Engineers and a member of the APWA Arizona Chapter. He can be reached at (520) 791-4259 or Richard.Nassi@tucsonaz.gov.
Michael J. Barton, P.E., PTOE, is the Transportation Business Group Manager with HDR Engineering, Inc., in Tucson. He has over 20 years of experience and is also a member of the National Committee on Uniform Traffic Control Devices, Signals Technical Committee. He is a Fellow of the Institute of Transportation Engineers. He can be reached at (520) 584-3647 or firstname.lastname@example.org.