Signalized Intersections: Appendix 4
European Strategies for Improving Signalized Intersection Safety
The Federal Highway Administration and the American Association of State Highway and Transportation Officials sponsored a scanning tour of several European countries in 2002. The purpose of the tour was to gather information about innovative practices for improving intersection safety and to evaluate the applicability of these practices for use in the United States. In addition to discussing innovative strategies with representatives from Sweden, Germany, the Netherlands, and the United Kingdom, the scanning tour team also discussed procedures for improving safety, implementing strategies, and operational and maintenance issues related to safety at signalized intersections. A full report on the scanning tour and the team's recommendations is forthcoming. In the mean time, a summary is provided on the FHWA web site1. An overview of the report is presented here; a summary table of the overview is provided at the end of this appendix (see Exhibit 8).
These are a few highlights from the European signalized intersection scanning tour; the scanning team found that generally the countries are emphasizing
The countries visited on the scanning tour are incorporating innovative treatments into their intersection safety programs that address red-light running, speeding, vehicles caught in the dilemma zone, and pedestrian safety concerns.
Photo enforcement of vehicle speeds and signal compliance is gaining popularity in the scanning tour countries, particularly Germany, the Netherlands, and the United Kingdom.
Germany uses cameras to enforce speeds on roadways and on intersection approaches, as well as compliance with traffic signals. The two main keys to success of automated enforcement in Germany are public information and significant fines for violations. Road signs and a public information campaigns inform drivers that cameras are being used for photo enforcement. Cameras are mounted in conspicuous locations so drivers are aware of their use. The penalties for speeding or disobeying the signal are substantial (hundreds of euros). Though the effectiveness of the photo enforcement program is still being studied, preliminary results at a number of intersections indicate that the strategy is effective.
Photo enforcement is also used in the Netherlands to enforce signal and speed limit compliance. As in Germany, camera visibility and public knowledge of their use are emphasized. The cameras are marked with red and blue stripes to increase their visibility (Exhibit 1). Signs are placed ahead of intersections with cameras to warn drivers of their use. Though the Dutch have not yet completed studies on the effectiveness of the cameras on improving safety, data have shown that violations at intersections with cameras have dropped to nearly zero, except for situations in which drivers have discovered that the cameras are not always being used (a fixed number of cameras is rotated through a larger number of camera housings; thus at any given time, some camera housings are empty). The drop in violations and corresponding drop in fines has meant that it is difficult for the camera equipment to be self-funding.
The United Kingdom also uses photo equipment to enforce speed and signal compliance but does not emphasize the need for camera visibility. Data suggest that this leads to a lower number of violations across a network rather than at a specific intersection. Since the cameras are not always conspicuous, violation rates do not drop as quickly as in other countries (such as the Netherlands, where cameras are more obvious), and there has not been significant problems generating enough revenue to cover the equipment purchase.
The United Kingdom has a well-defined framework for implementing automated enforcement in pilot study locations. Cameras should be installed only at high-accident locations and where speed is a main contributor to crashes, and speed studies should be conducted before cameras are installed in order to prove that speed is a problem at the site. The framework calls for coordination among police, courts, and local highway agencies. No organization is allowed to make a profit from use of the cameras, and the automated enforcement programs are subject to an audit each year.
Dilemma Zone Detection
Several European countries are implementing strategies to reduce the occurrences of vehicles being caught in the dilemma zone when a signal turns yellow.
Sweden uses a system called LHOVRA to improve safety at signalized intersections. LHOVRA comprises a series of detectors placed along an intersection approach. These detectors determine the vehicle type and speed, and this information is used to adjust the signal timing in order to minimize the number of vehicles caught in the dilemma zone (and therefore running a red light). This system is used mostly on rural intersections, especially where truck volumes are high. Study results show this strategy to be promising.
The Dutch use extensive networks of loop detectors placed in advance of intersections to adjust signal timings and thereby minimize motorists being caught in the dilemma zone. The detectors are used to modify green times on the basis of traffic demands and provide adequate green times for traffic to clear the intersection.
The United Kingdom uses a system called SDE (speed discrimination and extension) to avoid motorists getting caught in the dilemma zone and to minimize red-light running, particularly at higher-speed rural intersections. The U.K. defines the dilemma zone as the distance in which 10 to 90 percent of drivers stop when the signal changes to amber. The goal is to measure the occupancy of the dilemma zone on the major road approach. If it is occupied when a vehicle(s) is detected on the side street, the side street is not given a green signal until the vehicle(s) has cleared the intersection. The system times out at a maximum green time but only if it has already tried but failed to terminate early because the dilemma zone continued to be occupied.
The countries participating in the scanning tour use a variety of treatments for controlling speeds on signalized intersection approaches. Low-cost treatments for reducing speeds on approaches are discussed here.
At signalized intersections on higher-speed roadways (greater than 70 km/h), exclusive turn lanes and protected phasing are provided. On roadways with speeds between 50 and 70 km/h, shared lanes and permitted phasing are optional. For roadways with speeds of 90 km/hr or greater, acceleration lanes are provided for free-flow right turns. A tight turning radius is used to slow turning vehicles at intersections with heavy pedestrian traffic.
Sweden is also experimenting with portable variable-message signs in school zones. When a motorist approaches the school zone traveling at a speed that is greater than the posted speed limit, the sign lights up with a message that indicates the motorist is speeding in a school zone.
Sweden has also implemented the use of raised and virtually raised pedestrian crossings to slow vehicles approaching a crossing. Virtually raised pedestrian crosswalks are painted on the roadway surface and give the optical illusion of a raised surface. This approach is most effective and appropriate in locations where the majority of motorists are unfamiliar to the area (Exhibit 2).
To help address safety problems at high-speed intersections, the Germans place traffic signals and intersections with approach speed limits only less than 70 km/hr. On facilities with higher speed limits, either the crossings are grade-separated or the speed limit is lowered in advance of the intersections. Lowering the speed limit requires effective enforcement, and in many cases photo enforcement techniques have been used to successfully control approach speeds.
On roadways with speeds greater than 50 km/h, the Dutch use variable message signs to warn drivers if they are speeding as they approach an intersection (Exhibit 3). In addition, speed tables are often located just beyond the stop bar, as additional encouragement to reduce speeds. These speed tables are not used in areas with bus or heavy-truck traffic, but they are designed for passenger cars to be able to travel over them comfortably at low speeds (Exhibit 4).
Traffic signals in the Netherlands are set to dwell in the all-red mode when traffic is not present at an intersection. This practice has been shown to slow vehicles that are approaching intersections at high speed and is consistent with the overall safety practice and philosophy of reducing speed in potential conflict areas.
Roundabouts are a common intersection type in Europe, and the scanning tour team recommended they be considered as alternatives to signalized intersections as a way to reduce the severity of crashes.
Sweden has replaced some conventional signalized intersections with roundabouts in locations where accident severity is high. It is recognized that the overall accident rates may increase and sight distance be degraded, but the accident severity will decrease. Roundabouts often have a negative impact on the system because it is difficult to manage traffic systematically with roundabouts. Replacing signals with roundabouts seems to be motivated by political and police pressure.
In some cases, traffic signals have been installed at roundabouts. Signalizing roundabouts is not a preferred approach and is done on a very limited basis to improve pedestrian and bicyclist safety.
Germany uses roundabouts as an alternative to signalized intersections to reduce overall delay when approach volumes are balanced among all approaches. Single-lane roundabouts are preferred over multilane approaches and configurations, which are strongly discouraged. Mini-roundabouts are used in low-speed urban locations. The inner radius is 13 to 25 meters, and there is one lane, 4 to 4.5 meters wide. A raised island with a 4-meter radius is used. This intersection type has been shown to experience 60 percent less accidents than signalized intersections.
Roundabouts are typically not signalized in Germany. Signalizing roundabouts is considered a last resort and is used only in special circumstances to improve traffic flow, accommodate special pedestrian conditions, accommodate a trolley system, etc.
Only when there are no other options for addressing severe crashes at signalized intersections will the Dutch consider converting the intersection to a roundabout. Both single-lane and dual-lane roundabouts have been successfully implemented. Studies have shown a 60 percent increase in intersection safety performance. Roundabouts limit the ability to control traffic flow and maintain platoons in a network. Typically, upstream and downstream signals are used to control/meter traffic flow and improve the efficiency of the roundabout and the overall traffic network. Pedestrian and bicycle safety issues at roundabouts have been addressed by providing clearly delineated bicycle and pedestrian crossings.
The U.K. uses roundabouts extensively. Roundabouts with high volumes are frequently signalized. To address capacity issues, the U.K. uses several modified roundabout designs that provide for one or both through movements to travel through the middle of the roundabout. These modified designs have not yet been shown to impact safety.
The focus of some European countries on the safety of pedestrians and bicyclists has led to the development and implementation of innovative strategies for improving safety for nonmotorized road users at signalized intersections.
Many pedestrian crossings in Stockholm are equipped with acoustic indicators. The devices serve two purposes. First, hey reinforce the visual crosswalk indicators by emitting a fast ticking sound during the green pedestrian phase, an even-faster ticking during the pedestrian-clearance phase, and a slow ticking during the red pedestrian phase. Since the same ticking sounds are used on both streets, it is essential that the speakers emitting the sound be mounted quite closely and directionally to the pedestrians waiting at each of the crosswalks. The Team felt this was a particularly effective approach (much superior to the bird chirping sounds used in the United States). Second, they provide clear walk and don't-walk indications for the visually impaired. Additionally, some pedestrian-crossing push-buttons are equipped with a special locator tone that helps the visually impaired locate the button (Exhibit 5).
As with other European countries, the Germans place a very high priority on bicycle and pedestrian traffic safety and protecting vulnerable road users. In some cases, pedestrians and bicyclists are given priority over motorized vehicle traffic.
Audible pedestrian signals are used to supplement signal indicators. The audible signals are designed with a variable-volume feature that is controlled by the surrounding traffic noise; as the level of traffic noise increases, so does the volume of the audible crossing signal.
Countdown timers seem to be an effective way of providing positive reinforcement to nonmotorized traffic-that the pedestrian timing button has been activated and the signal is operating properly. Among several devices is an indicator that surrounds the pedestrian push button (Exhibit 6). The yellow lights surrounding the push button darken sequentially (i.e., "count down") to let the pedestrians know their wait is ending.
Several innovative signalized pedestrian crossings are used in the United Kingdom. One such crossing type is the PUFFIN pedestrian user-friendly intelligent) system. When a pedestrian call button is activated, a detector is used to determine whether a pedestrian is present at the curbside. If so, the pedestrian phase is called and a light is illuminated to inform the pedestrian that a call has been made for a crossing signal. If the pedestrian crosses on red, the detector notifies the system, and the call for the phase is cancelled. During a crossing phase, pedestrians are monitored on the crosswalk so that they are given sufficient time to cross (Exhibit 7). This same technology is also being applied to bicycle crossings, called TOUCAN crossings ("two can" cross).
Exhibit 8 summarizes the strategies observed in four European countries and recommended by the scanning tour group.