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17 by making three consecutive right turns. Along some LRT alignments, there may be few locations where left turns are permitted across the tracks, which could lead to increased pressure for motorists to turn left where left turns are possible, even if they are prohibited. Posting advanced signs showing motorists that they can accomplish upcoming left turns by making three consecutive right turns starting beyond the cross street might help reduce the number of left-turn violations. This can be iterated in public education materials by including instructions for accomplishing a left turn by making three suc- cessive right turns (4). FIGURE 19 Use of green arrow aspects for through traffic. SIGNAL DISPLAYS In-Roadway Lights Red Left-Turn Arrows In-roadway lights are defined in the MUTCD (10) as "special Red left-turn arrows (as shown in Figure 18) provide more types of highway traffic signals installed in the roadway surface positive guidance to motorists than red balls. At a few inter- to warn road users that they are approaching a condition on or sections in Denver with LRT, where left turns are made from adjacent to the roadway that might not be readily apparent a one-way street onto another one-way street, left turns on red and might require the road users to slow down and/or come are not allowed owing to the LRT tracks. In RTD's experi- to a stop" (10). In 2006, Houston METRO began testing an ence, the red left-turn arrow signal display has worked better application of in-roadway lights to get motorists' attention than the combination of a red ball and static signs stating "No to stop at the red lights on the cross-street approaches to sig- Turn on Red." Motorists seem to have more respect for the red nalized intersections with LRT and to reduce encroachment arrow signal display than the static sign, as they will violate into the intersection. The lights being tested by METRO are the signs more often than the signals. red, installed along the stop bar, and flicker at a fast rate. An application of the in-roadway lights at one intersection in Green Arrow Aspects for Through Traffic Houston is illustrated in Figure 21, as an LRV approaches from the right. In an effort to provide positive guidance, the METRORail Traffic Safety Assessment report recommended the use of Over the past year, METRO has installed in-roadway green arrow aspects on traffic signal heads instead of green lights at 11 intersections and experienced only two red-light balls and redundant turn-prohibition signs (4) (Figures 19 running accidents at the 11 intersections since installation (the and 20). Coifman and Bertini also recommend the use of green lights have been installed at the intersections on average for arrow aspects for through traffic to reduce the chance that a about 11 months). This compares with about eight red-light driver turning left will mistake the through traffic signals for running accidents per year on average at these same inter- the turning movement, which can happen for a number of rea- sections for the previous 3-year period, a reduction METRO sons. First, there are generally more through signals than turn views as significant. arrows. Second, the surface area of the green ball is greater Although this application was to prevent red-light running than the surface area of an arrow, making it more prominent. on the cross street, it could have the same effect, for some align- Third, the transmittance of a green filter is greater than that of ments, for left-turning traffic. LACMTA reported that they are a red filter. For these reasons, the through traffic signal balls currently considering using the in-roadway lights to mitigate have a greater probability of being perceived by a driver than left-turn motorist violations at intersections with LRV. do the left-turn arrow signals (3). If green arrow aspects are used for through movements, a green ball should still be used in the right lane where right turns are permitted across the par- allel crosswalk pedestrian movement. FIGURE 18 Use of a red arrow to prohibit the left-turn movement. FIGURE 20 Use of arrows to control traffic movements.