Introduction to Transport

1. Introduction to Transport Lecture 7: Signal Coordination

2. Signal Progression in 1-way street • Determining ideal offset Assuming no vehicles are queued at the signals, the ideal offsets can be determined assuming a desired platoon speed of 60 fps.

3. Signal Progression in 2-way street • Determining ideal offset If any offset is changed to accommodate the southbound vehicle then the northbound movement will suffer.

4. Signal Progression in 2-way street • Offsets in a two-way arterial are not independent. • A typical cycle yields the obvious conclusion that the offsets in two directions adds up to the cycle length. • However, for longer block lengths the offsets might add to two (or more) cycle lengths. Indeed, when queue clearances are taken into account, the offsets might add to zero cycle lengths.

5. Signal Progression in Grid The relative difficulty of finding progressions on a two-way street, compared to on a one-way street, might lead one to conclude that the best approach is to establish a system of one-way streets, to avoid the problem.  A one-way street system has a number of advantages, not the least of which is elimination of right turns against opposing traffic. However, the total elimination of the constraints imposed by the "closure" of loops within the network or grid is not possible. If the cycle length, splits, and three offsets are specified, the offset in the fourth link-denoted Link D in this Illustration is determined and cannot be independently specified.

6. Signal Progression in Grid This extends to a grid of one-way streets, in which all of the north-south streets are independently specified. The specification of one east-west street then "locks in" all other east-west offsets. Note that the key feature is that an open tree of one-way links can be completely independently set, and that it is the closing or "closure" of the open tree which presents constraints on some of the links.

7. Signal Progression in Grid

8. Signal Progression in Grid

9. Signal Progression in Grid While it is sometimes necessary to consider networks in their entirety, it is common traffic engineering practice to decompose networks into non-interlocking arterials whenever possible.

10. Bandwidth

11. Bandwidth

12. Signal Progression

13. Expected questions • Theory Junction, junction design Traffic signs (classification and details) Types of traffic signal control (description and comparison) Discharge headway, different types of lost time Different types of capacity calculation Delay Bandwidth, Progressions • Numerical Problems Traffic signal design Area traffic control All examples given in lectures