Development of Left-Turn Lane Warrants for Unsignalized Intersections (2013) / Chapter Skim
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Pages 63-82
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61 CHAPTER 4 DRIVER BEHAVIOR STUDY BACKGROUND While many intersections in urban environments are signalized, numerous intersections are unsignalized and have considerable left-turn activity. Particularly in areas with dense development, left-turn movements can be problematic because a wide variety of activity (through traffic, pedestrian traffic, parking maneuvers, etc.)
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62 • Signal coordination -- location is near enough to a signal to be affected or far enough from a signal to result in random arrival; and • Approach speed range -- low or high speed, with posted speed limits between 25 and 40 mph being defined as low speed and posted speed limits of 45 mph or more being defined as high speed. Table 38 lists the 30 sites used in this study and their corresponding geometric characteristics.
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63 Table 38. Site characteristics.
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64 (a) Elevated video cameras (b)
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65 Table 39. Time-to-clear and time-to-turn values for passenger cars starting from a stopped position at each site.
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66 Figure 14 shows each site's average turning time by crossing distance, subdivided by the number of lanes and the presence of a left-turn lane (LTL)
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67 Table 40. Comparisons of turning times for passenger cars.
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68 • Crossing width (ft) , • Number of lanes (crossing either one or two lanes)
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69 Table 41. Regression model for turning time.
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70 Variables Low Value Middle Value High Value Accepted Lag/Gap Time (sec) Time @ Head of Queue (sec)
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71 (a) Contribution of Variable to Turning Time (b)
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72 Variables Assumed Value Accepted Log/Gap Time (sec) Time @ Head of Queue (sec)
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73 A similar condition existed for time in the queue. Expectations were that drivers would drive faster after waiting in a queue.
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74 βo, β1 = regression coefficients. The logistic function can be converted to a linear form with the following transformation: ݃ ሺݔሻ ൌ ݈݃ ሺ௫ሻଵିሺ௫ሻ ൌ ሺߚ ߚଵݔሻ (18)
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75 Table 42. Logistic regression coefficients for field sites.
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76 Figure 18. Plot of logit model for three field sites.
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77 Table 43. Results for gap acceptance methods.
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78 Table 44. Mean values of gap (sec)
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79 Figure 20. Plot of median gap acceptance for 25-mph and 55-mph sites from this field study and Yan et al.
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80 Figure 22. Gap acceptance result by crossing distance group for field study sites.
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