How does TNM compute acceleration on roadways with traffic-control devices?
For TNM roadways with a traffic-control device, TNM computes accelerating speeds along the roadway’s length as a function of vehicle type and roadway grade until the final speeds are attained or the end of the roadway is reached. For the next roadway, TNM begins anew with that roadway’s input speeds. In other words, while TNM tracks speeds from one roadway segment to the next, it does not link speeds from one roadway to the next. If you know that vehicles will continue to accelerate past the endpoint of the TNM traffic-device roadway, you must extend this roadway if you wish to allow for continuing acceleration. For example, if heavy truck acceleration will continue past the physical merge point of an on-ramp with the mainline, you may wish to extend the on-ramp past this physical merge point, parallel to the mainline, so that heavy trucks will come close to reaching input speed before the end of the on-ramp roadway. Use Figure 45 on Page 57 of the TNM Technical Manual to compute this
