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From page 11... ... 11 C H A P T E R 3 3.1 Introduction Four of the 16 research topics covered in this report are related in that they involve "interrupted flow," that is, the deceleration, acceleration, and possible stopping and idling of vehicles. The topics are signalized interchanges, intersections, roundabouts, and area sources. Read the entire page →
From page 12... ... 12 • Use of yield signs at the entries rather than stop signs or signals. The goal of modern roundabout design is to slow, but not stop, the vehicles, achieving smooth and safe functioning of the intersection. Read the entire page →
From page 13... ... 13 on the traffic tab of the roadway input dialog box are treated by FHWA TNM as the final speeds that vehicles will try to reach during their acceleration. The modeler provides a starting speed for all traffic on the roadway, called the "speed constraint," which would be zero for a stop sign, but which could be non-zero for an entrance ramp, as an example. Read the entire page →
From page 14... ... 14 idling while the signal is red before acceleration begins when the signal turns green? • When is this entire effort worth doing? Read the entire page →
From page 15... ... 15 sound levels that can be expected with changes in the FHWA TNM Flow Control input parameters for acceleration and the NCHRP Report 311 guidelines for deceleration. From these results, initial guidelines were developed on the modeling of components of roundabout approach and departure legs and inner circulatory roadway. Read the entire page →
From page 16... ... 16 acceleration region and on into the cruise speed region is only about 2 dB. The FHWA TNM roadway segment lengths should not exceed 50 ft if the final cruise speed is 30 mph, 100 ft for 45 mph, and 500 ft for 60 mph or higher. Read the entire page →
From page 17... ... 17 700 ft on a 0% grade -- for the above-cruise speeds and truck percentages. Appendix B provides details on this analysis. Read the entire page →
From page 18... ... 18 ramp traffic counted during three of the four measurement periods factored up to hourly volumes. The deceleration was modeled using the NCHRP Report 311 segment lengths and speeds for deceleration from 60 to 0 mph acceleration at the end of the ramp, and local road traffic are not modeled. Read the entire page →
From page 19... ... Figure 11. Diamond interchange Leq(h) Read the entire page →
From page 20... ... 20 Figure 13. Traffic signals control the flow on either side of the interchange. Read the entire page →
From page 21... ... 21 similar flow control roadways for traffic moving in the opposite direction on the crossing road. A disadvantage of this detailed modeling is that it requires modeling of 12 intersecting points of the ramp sections and the cross street roadways, all set as "on structure" segments to allow the mainline roadways to pass under them. Read the entire page →
From page 22... ... 22 For the left-turn movement (C) , the flow control acceleration roadway is started past the center of the interchange with 50% Vehicles Affected due to the presence of the signal, which is on the entrance (western) Read the entire page →
From page 23... ... 23 at a typical intersection of two two-lane roads. The separation would be greater for the SPUI. Read the entire page →
From page 24... ... 24 be modeled by FHWA TNM roadways in each direction at cruise speed with no acceleration or deceleration. The cross street probably does not need to be modeled because if even a four-way stop is not warranted to control traffic on the main road, then intersecting road volumes and speed are both likely to be low. Read the entire page →
From page 25... ... 25 Figure 18. Read the entire page →
From page 26... ... 26 stopping point back to an upstream distance of 600 ft by the following: • 25% Affected: 0.4 to 0.8 dB. • 50% Affected: 0.6 to 1.6 dB. Read the entire page →
From page 27... ... 27 30-mph cases, there is symmetry on the approach and departure legs caused by the accelerating traffic in each direction. The largest differences at the 50-ft receiver offset distance are on the order of 1 dB. Read the entire page →
From page 28... ... 28 about would begin. Figure 21 also shows a departure FHWA TNM roadway (dotted line) Read the entire page →
From page 29... ... 29 • Case 1 included full modeling of all four legs of the roundabout using NCHRP Report 311 deceleration segment lengths and speeds for 40 to 0 mph on the approaches, a circulatory road speed of 15 mph, and FHWA TNM acceleration on the departures. • Case 9 included the same deceleration modeling as Case 1 for the western, northern, and southern legs, but no traffic on the eastern legs or the circulatory road. Read the entire page →
From page 30... ... 30 Essentially, the noise of accelerating traffic on the departure side of the roundabout dominates the measured Leq on both sides of the road, supporting the sensitivity analysis conclusion. 3.4.6.3 Two-Lane Inner Circulatory Road A roundabout with a two-lane inner circulatory road may be modeled in essentially the same way as a one-lane inner circulatory road. Read the entire page →

From page 11...

... 11 C H A P T E R 3 3.1 Introduction Four of the 16 research topics covered in this report are related in that they involve "interrupted flow," that is, the deceleration, acceleration, and possible stopping and idling of vehicles. The topics are signalized interchanges, intersections, roundabouts, and area sources.