Superelevation Criteria for Sharp Horizontal Curves on Steep Grades (2014) / Chapter Skim
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20 S E C T I O N 3 Three types of field studies were conducted as part of this research. Results of the field studies were used as inputs into the vehicle dynamics simulation models and/or served to validate the model outputs.
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21 either approaching the curve or in the curve. Similarly, the super elevation represents the maximum superelevation on the curve.
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22 • Subject vehicles tracked from the rear as they drove away from the laser gun. Figure 9 illustrates the general field setup for the speed studies.
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23 • Trucks: – Single-unit truck – Tractor semi-trailer truck – Tractor semi-trailer/full-trailer truck (double) While collecting speed data, one or two video cameras were also positioned on the roadside to record vehicle maneuvers at the sites.
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24 0 4 8 C A 1 0 4 8 C A 2 0 4 8 C A 3 0 4 8 M D 1 0 4 8 M D 2 0 4 8 M D 3 0 4 8 PA 1 0 4 8 PA 2 0 4 8 W A 1 -2440 -2040 -1640 -1240 -840 -440 -40 360 760 1160 1560 1960 2360 2760 0 4 8 Pe rc en t Pe rc en t Pe rc en t Pe rc en t Pe rc en t Pe rc en t Pe rc en t Pe rc en t Pe rc en t Pe rc en t W A 2 Distance from Point of Curvature (ft) Figure 11.
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25 0 4 8 W A 3 0 4 8 W A 4 0 4 8 W A 5 0 4 8 W A 6 0 4 8 W A 7 0 4 8 W V 1 0 4 8 W V 2 0 4 8 W V 3 0 4 8 Pe rc en t W V 4 -2440 -2040 -1640 -1240 -840 -440 -40 360 760 1160 1560 1960 2360 2760 0 4 8 Pe rc en t Pe rc en t Pe rc en t Pe rc en t Pe rc en t Pe rc en t Pe rc en t Pe rc en t Pe rc en t W V 5 Distance from Point of Curvature (ft) Figure 11.
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Site Posted speed limit/ advisory speed (mph) Avg veh count 500 ft upstream of curve Beginning of curve (i.e., PC)
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27 Dist (ft) Passenger vehicles Trucks # of Obs Avg speed (mph)
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28 most sites, less than 10% of the vehicles changed lanes near or on the curve. At two of the sites (MD1 and WV1)
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29 Site Left maneuver (s) Right maneuver (s)
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30 The degrees of freedom were calculated using the Welch- Satterthwaite equation, and variance components were used for the variance-structure of the split-plot model. Main effect results are shown in Table 14, and statistically significant interaction effects are shown in Table 15.
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31 at different levels of another main effect. All inter action effects were tested in this model, but only two were found to be statistically significant.
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32 The instrumented vehicle was driven behind vehicles in the traffic stream chosen randomly but selected such that the vehicles were not following other vehicles that would influence their speed. The instrumented vehicle was maintained at a constant following distance -- approximately 300 ft behind the lead vehicle as shown in Figure 13.
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33 the grades as reported on profile sheets for the sites. As an example, the measured grades were inferred from the height (z)
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34 a high level of agreement between the instrumented vehicle data and the actual roadway plans. After it was confirmed that the in-vehicle geometric measurements agreed well with horizontal and vertical alignment information obtained from roadway plans and profiles, the horizontal and vertical alignment data were imported into CarSim to simulate the vehicle's dynamics to compare simulation results to instrumented vehicle measurements.
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35 information obtained from plans and profiles (and/or a combination of roadway inventory files and field measurements)
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36 Several general findings regarding the speed data collected from the instrumented vehicle are as follows: • Overall, the mean speed profiles measured by the instrumented vehicle agreed with the speed data collected from the laser guns. • The variability in the vehicle acceleration within a curve was approximately between 3 and -3 ft/s2; this magnitude is consistent with the curve-entry deceleration reported by Bonneson (2000b)
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37 section of the report (1) explains the data collection methodology used to collect friction data in the field, (2)
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38 of normal travel and slight deceleration. All friction measurements on the approach tangent were taken in the left wheel path.
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39 1,2,3 450 ft Close-up of measurement locations 150 ft 150 ft 150 ft First Segment (approach) Second Segment (curve)
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