National Academies Press: OpenBook

Light Rail Vehicle Collisions with Vehicles at Signalized Intersections (2008)

Chapter: Chapter Two - Collisions Between Light Rail Vehicles and Motor Vehicles at Signalized Intersections

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Suggested Citation:"Chapter Two - Collisions Between Light Rail Vehicles and Motor Vehicles at Signalized Intersections." National Academies of Sciences, Engineering, and Medicine. 2008. Light Rail Vehicle Collisions with Vehicles at Signalized Intersections. Washington, DC: The National Academies Press. doi: 10.17226/14215.
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Suggested Citation:"Chapter Two - Collisions Between Light Rail Vehicles and Motor Vehicles at Signalized Intersections." National Academies of Sciences, Engineering, and Medicine. 2008. Light Rail Vehicle Collisions with Vehicles at Signalized Intersections. Washington, DC: The National Academies Press. doi: 10.17226/14215.
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Suggested Citation:"Chapter Two - Collisions Between Light Rail Vehicles and Motor Vehicles at Signalized Intersections." National Academies of Sciences, Engineering, and Medicine. 2008. Light Rail Vehicle Collisions with Vehicles at Signalized Intersections. Washington, DC: The National Academies Press. doi: 10.17226/14215.
×
Page 8
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Suggested Citation:"Chapter Two - Collisions Between Light Rail Vehicles and Motor Vehicles at Signalized Intersections." National Academies of Sciences, Engineering, and Medicine. 2008. Light Rail Vehicle Collisions with Vehicles at Signalized Intersections. Washington, DC: The National Academies Press. doi: 10.17226/14215.
×
Page 9
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Suggested Citation:"Chapter Two - Collisions Between Light Rail Vehicles and Motor Vehicles at Signalized Intersections." National Academies of Sciences, Engineering, and Medicine. 2008. Light Rail Vehicle Collisions with Vehicles at Signalized Intersections. Washington, DC: The National Academies Press. doi: 10.17226/14215.
×
Page 10

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6The placement of LRT in the middle of, adjacent to, or within an urban street can lead to complex crossings incorporated into signalized highway intersections. Although these intersections are typically protected with conventional traffic signals and supplemental signage regarding the LRT, they do not operate like conventional crossings, nor do they operate like conven- tional signalized intersections. Rather, they are intersections with unique operating characteristics that have proven to create problems that can lead to collisions between LRVs and motor vehicles, especially when turning maneuvers are involved. LIGHT RAIL TRANSIT ALIGNMENT THROUGH SIGNALIZED INTERSECTIONS The diagrams in Figure 1 illustrate a few examples of how LRT can be incorporated into urban street signalized inter- sections. The diagrams include a median-running alignment, two side-running alignments, and a mixed-use alignment. Although each of the diagrams shows dual tracks, any of these alignments could include single-track operation and other vari- ations in the number of traffic lanes where there are traffic movements. These diagrams are shown for example purposes only. Even though there are common challenges among the different alignments, each presents its own unique challenges, which are discussed in more detail here. Median-Running Alignments In median-running alignments (Figure 1a), LRVs operate between the parallel, two-way lanes of an urban street. The LRT right-of-way typically is unpaved (except at designated locations where motor vehicles cross the light rail tracks) and is separated from the roadway by curbs, and in some cases, fencing. Left-turn pocket lanes for motor vehicles are typically provided in the parallel running roadways. Motor vehicle movements are controlled by traffic signals. Left-turn motor vehicle movements are protected through the use of left-turn- only traffic signal phases so as to control motor vehicle move- ments that conflict with LRVs. Reports of violations of the left-turn signal by motorists are not uncommon at these inter- sections. Collisions typically occur when motorists disregard, do not perceive, or misinterpret the left-turn signal and are unaware that an LRV in the median is approaching the inter- section from behind. Although less common, collisions also occur when a motorist intending to turn left at an intersection turns in front of an LRV approaching the intersection from the opposite direction. Cross traffic red-light running is also of concern at these intersections. Side-Running Within Roadway Right-of-Way Side-running LRT within the roadway right-of-way (Figure 1b) operates on a paved guideway within the roadway boundaries of one-way streets. The LRT guideway may be separated from the roadway by a curb or other physical features except for where motor vehicles must cross the light rail tracks to turn onto the cross street. Challenges encountered at these inter- sections are dependent on whether the LRT right-of-way is located to the left or right of the one-way traffic running parallel to the tracks. With LRT alignments to the left of the roadway, left turns in front of LRVs approaching on the left from behind are the most prevalent accident type, as motorists may be unaware of the presence of the LRV. Similarly, right turns in front of LRVs approaching on the right from behind are the most common incidents occurring when LRT align- ments are to the right of the roadway. As with other inter- sections, cross-street traffic disobeying traffic signals can also be problematic. Side-running alignments have the added challenge of vehicles encroaching onto the tracks where the tracks cross the cross-street approach. Side-Running Adjacent to Roadway Side-running adjacent to a roadway (Figure 1c) are LRT align- ments located outside of a roadway right-of-way. As with side- running LRT alignments within the roadway right-of-way, the guideway may be physically separated from the roadway by a curb, landscaping, and/or fencing. Unlike side-running within the roadway right-of-way, two-way traffic flow on the adja- cent roadway is common. Challenges are similar to those of side-running within the roadway right-of-way—motorists turning in front of LRVs approaching an intersection from behind the motorist, vehicles encroaching onto the tracks on the cross-street approach, and motorists running red lights on the cross-street. Mixed-Use Alignments Generally in mixed-use alignments (Figure 1d), motor vehi- cles and LRVs share the same travel lanes. It is not uncom- CHAPTER TWO COLLISIONS BETWEEN LIGHT RAIL VEHICLES AND MOTOR VEHICLES AT SIGNALIZED INTERSECTIONS

7mon, however, for lanes to be designated as “LRV Only” lanes, with vehicular traffic running parallel to the LRT right-of-way. The LRV-only lane is differentiated from the roadway by sign- age and striping, contrasting colored pavement, mountable curb, rumble strips, traffic buttons, or other tactical treatment. Motor vehicle turning movements for parallel running traffic may be from the same lane in which the LRV is operating or from the adjacent lane to the LRT. In either case, only when it is clear and LRV operators are assured that there are no conflicting moves, are they required to proceed through the intersection with caution. Conflicting turning movements may be controlled by displaying red traffic signals for all directions of motor vehicle traffic when an LRV is passing through the intersection, by permitting the conflicting move only after the LRV has passed through the intersection, or by prohibiting turning movements across the LRT altogether. Challenges in mixed-use alignments are similar to those without LRT oper- ations: motorist attempts to overtake and turn left in front of LRVs, motor vehicle traffic from the opposite direction turning suddenly in front of an approaching LRV, and cross traffic violating the red traffic signal. PROBLEMS BETWEEN LIGHT RAIL VEHICLES AND MOTOR VEHICLES AT SIGNALIZED INTERSECTIONS The 1996 review of 10 LRT systems for TCRP Report 17 iden- tified the principal problems between LRVs and motor vehicles at signalized intersections. These problems covered a range of issues, including LRT alignment and complex intersection (a) (b) (c) (d) FIGURE 1 Examples of common LRT alignments through signalized intersections: median-running (a), side-running within roadway right-of-way (b), side-running adjacent to roadway (c), and mixed-use (d ).

geometry; traffic signal timing and pre-emption of the left-turn phase; and driver factors such as expectancy, confusion, and risk-taking (1). These issues could play a role in the occurrence of LRV–motor vehicle collisions. Although these issues were identified in the research conducted more than 12 years ago, most of these issues are challenges that many transit agencies still experience today. ROLE OF THE MOTORIST IN LIGHT RAIL VEHICLE–MOTOR VEHICLE COLLISIONS Transit agencies with LRT systems consistently report that most collisions between LRVs and motor vehicles are caused by motorists making illegal or improper turns or running red lights. Although there have been special considerations given to safety in the design and operation of LRT systems, motorists continue to exhibit risky behavior and ignore traffic control devices at LRT crossings. In a working paper developed for California Partners for Advanced Transit and Highways (PATH) (3), the authors reported that one of four critical events on the part of the motorist must occur before a left-turn collision with an LRV at a median-running crossing. These critical events include: • Disobedience—An inappropriately low perception of risk and expectations from conventional intersections contribute to driver disobedience. For example, motorists may violate static “No Turn on Red” signs at conven- tional intersections with little to no consequences; how- ever, when the perception of risk and expectation from this situation at a conventional intersection is transferred to an intersection with LRT, the same action can have more serious consequences. • Failure to perceive—This occurs when motorists do not observe the traffic control devices. For example, a motorist who sees the adjacent through-traffic’s signal turn green and the through vehicles proceed into the intersection may not perceive that the left-turn signal is red owing to an approaching LRV. • Misinterpretation—Misinterpretation accidents are related to expectation errors and cognitive limitations of motorists, and they can be more likely to occur at complicated intersections such as those that incorpo- rate LRT. • Violation of drivers’ expectations—When driver expec- tancy is violated, it can lead to accidents. Drivers grow accustomed to intersections operating in a certain way, which may lead them to anticipate movements. For example, in an area where leading left turns are used pre- dominately, a collision between an LRV and a motorist turning left could occur if the motorist proceeds into the intersection in anticipation of the leading left-turn phase only to discover that it has been pre-empted by an approaching LRV. In other words, drivers’ expectations affect driver behavior. 8 TYPES OF COLLISIONS OCCURRING BETWEEN LIGHT RAIL VEHICLES AND MOTOR VEHICLES AT SIGNALIZED INTERSECTIONS Collision types and circumstances tend to vary between agencies, depending on a variety of factors including the envi- ronment, the initial incorporation of LRT into the city streets, driver types and attitudes, and traffic control. Consequently, accident type prevalence differs among transit agencies. However, transit agencies with LRT systems consistently report that most collisions between LRVs and motor vehicles are caused by motorists making illegal or improper turns or running red lights. Left-Turn Collisions Motor vehicles that make illegal turns in front of approach- ing LRVs account for the greatest percentage of total colli- sions for most LRT systems (5). Data from 1998 show that motorists making improper left turns in front of light rail trains caused 62 accidents, 47% of all LRV–motor vehicle accidents. This accident occurrence pattern is not specific to intersections with LRT, but is consistent with motor vehicle accident experience at intersections in general. The Califor- nia Public Utilities Commission found that the second most common cause of LRV–motor vehicle accidents was the problem of motor vehicles running red lights or driving around gates (6). In a traffic safety assessment that took place 1 month after Houston’s METRORail began operation, researchers stated that the most common type of collision between motor vehi- cles and METRORail vehicles involved illegal left-hand turns by motorists. Despite traffic signs and signals designed to control the location and timing of left-turn movements along the rail line, several motorists turned into or in front of oncoming LRVs, sometimes turning from an incorrect lane. All collisions examined appeared to have been the result of improper or illegal turns or other driver errors. Illegal left turns are a primary source of motorist–LRV collisions in other light rail systems as well (5). Right-Angle Collisions A paper presented at the 2006 APTA Rail Conference dis- cusses stop bar violations on the cross-street approaches to intersections with LRT crossings (7). It describes the special considerations given to safety in the design and operation of the LRT system; however, motorists continue to exhibit risky behavior and ignore traffic control devices at LRT– roadway crossings. Risky behavior includes the failure of motorists to acknowledge traffic signals, to obey active warning devices, and to stop within clear zones—all of which can lead to right-angle collisions between LRVs and motor vehicles.

9COMMON LIGHT RAIL VEHICLE–MOTOR VEHICLE COLLISION SCENARIOS Considering the many different types of street-running oper- ations of LRT, there are many different scenarios of possible collisions between LRVs and motor vehicles at signalized intersections. However, the most common types of collisions are motor vehicles making illegal or improper left turns in front of LRVs and right-angle collisions with vehicles on the cross streets; therefore, they are the focus of this synthesis. Based on a review of the most recent literature and inter- views with selected transit agencies for this research, the most common scenarios of left-turn and right-angle colli- sions at signalized intersections can be categorized as the following: • Motorists in left-turn pocket lanes violate the red left- turn signal indication and collide with LRVs approach- ing from behind. • Motorists make illegal left turns against static no left- turn signs (at locations where turns are prohibited) and collide with LRVs approaching from behind. • Motorists violate active turn-prohibition signs and train- approaching warning signs in conflict with LRV opera- tion (at locations where turns are permitted/prohibited). • Motorists make left turns from adjacent through-only lanes instead of from the lanes shared with the LRVs (mixed-use). • Drivers encroach on or stop on the tracks and are struck by an LRV (coming from either direction) at a right angle (side-running alignment only). • Drivers run a red signal indication and collide with an LRV (coming from either direction) at a right angle. Table 2 presents each of these six collision scenarios along with a list of possible causes of each scenario. The following section presents a number of countermeasures that can be implemented to mitigate the occurrence of these collision scenarios.

10 Collision Scenario Possible Causes Signs do not convey to motorists why they are not allowed to turn. Motorists initiate their left turns against the signal as soon as the cross-street traffic receives the red (particularly common at locations with leading left-turn phases). Motorists in the left-turn lane mistake the through-traffic signals for those controlling the left-turn movement. Motorists in the left-turn lane cue off of the movement of the through vehicles. Motorists make left turns across the LRT right-of-way immediately after termination of their green left-turn arrow. Motorists confuse LRT signals with traffic signals. Motorists in left-turn pocket lane violate the red left-turn signal indication and collide with LRVs approaching from behind. Where traffic signals are pre-empted during the left-turn phase, motorists may incorrectly assume that the signal failed and violate the signal. There may be too few locations to make left turns across the tracks leading to increased pressure to turn left where such movements can be made, even if prohibited. Left turns were previously allowed before the LRT system was constructed. Permanently prohibiting a traffic movement that was previously allowed disrupts normal, expected travel patterns. Motorists who are used to violating regulatory signs with little consequence at conventional signalized intersections need to better understand the risks of violating turn prohibitions at intersections with LRT. There are too many signs at intersections. Multiple signs increase driver information processing time and increase the potential for missing important information. Motorists make illegal left turns against static no left-turn signs and collide with LRVs approaching from behind. Traffic control devices place an emphasis on prohibited rather than permitted movements. Drivers may be confused about where they can make turn movements and where a through movement is the only permitted movement. Signs may be activated too far in advance of the LRV arrival. If motorists perceive that the LRVs do not come even when the signs are active, they may lose respect for the signs and turn in conflict with an LRV. Signs may be activated too late to provide sufficient advance warning to motorists. Motorists violate active turn- prohibition signs and train- approaching warning signs in conflict with LRV operation. Motorists do not understand why the signs are on and/or why turns are prohibited. Permitting movements at some times and prohibiting them at others causes driver confusion. Motorists make left turns from through lanes instead of adjacent or lanes shared with the LRVs. Drivers are confused about which lane to turn from. Failure to understand the proper behavior at these locations may lead to vehicle–train conflicts. Having too many transverse markings on the roadway in the vicinity of the intersection (e.g., crosswalk, stop line, railroad markings) can cause confusion about where to stop. Motorists may not perceive the LRT tracks crossing the roadway on the approach to the intersection. Drivers encroach on or stop on the tracks and are struck by an LRV (coming from either direction) at a right angle. Motorists attempt right or left turns on red and stop on the tracks to wait for a gap in traffic as the LRV approaches. Drivers run a red signal indication and collide with an LRV (coming from either direction) at a right angle. Motorists are unaware an LRV is coming or speed through the intersection in an attempt to beat an approaching LRV. TABLE 2 COMMON COLLISION SCENARIOS AND POSSIBLE CAUSES

Next: Chapter Three - Countermeasures to Mitigate Collisions Between Light Rail Vehicles and Motor Vehicles at Signalized Intersections »
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TRB's Transit Cooperative Research Program (TCRP) Synthesis 79: Light Rail Vehicle Collisions with Vehicles at Signalized Intersections explores mitigation methods tested and used by transit agencies to reduce collisions between light rail vehicles (LRVs) and motor vehicles where light rail transit (LRT) runs through or adjacent to highway intersections controlled by conventional traffic signals.

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