Return to Traffic Engineering Design  Traffic Engineering Design    Project Summary ::   1  2  3  4   Background The NH 120 corridor in Lebanon, New Hampshire is a primary commuting route for several major employers (e.g. Dartmouth-Hitchcock Medical Center, Dartmouth College, Centerra Business Park). In order to maximize traffic flows during the major commuting periods, Resource Systems Group created a four-signal coordinated signal timing plan to minimize delay and queues during the AM and PM peak periods. Of special concern were frequent AM peak period queues at the I-89 ramps that extended beyond the ramps and onto the interstate. Project Scope •  Developed AM and PM peak hour analysis volumes •  Incorporated planned geometric changes along two of the minor legs •  Utilized microsimulation software to estimate delay and queue lengths under various cycle-split-offset combinations during the AM and PM peak periods •  Implemented the new signal timing plans in the field •  Visited the NH 120 corridor several times to fine-tune the system with field adjustments Project Results The new AM and PM peak period signal timing plans were implemented along the NH 120 corridor in the spring of 2005. There have been no reports of AM peak period queues extending onto the interstate since then. In coordinated systems, the major movements often receive more green time at the expense of the minor legs. After the signal timings were implemented, we recognized that school buses using the minor leg at Heater Road were being delayed. Thus, a niche timing plan that extended the minor leg green time for a short period was created to accommodate these school buses without creating undo delay for the major movements along NH 120.