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Posted on: January 25, 2017

UMD Study on Potential Traffic Impact of the Bethesda Downtown Plan

Last October, the Town commissioned a study by the University of Maryland National Transportation Center on the potential impact of the proposed Bethesda Downtown Plan on area traffic.  This report, available here, has just been completed and submitted to the Town.  Following are some key findings in the report.

  1. Even without any development, congestion on major arteries in Bethesda is bad and will get worse over the life of the Plan.

  2. The additional development that will come with the Plan will make congestion even worse.  For example, the time to travel southbound on Wisconsin Avenue from the Capital Beltway to the D.C. line during the afternoon rush hour will increase from approximately 8 minutes to 16 to 19 minutes (depending on the assumptions).  Similarly northbound traffic on Connecticut will increase from 13 minutes to 24 to 34 minutes (depending on the assumptions).  All major arterial routes will suffer similar congestion.

  3. The traffic modeling is particularly sensitive to whether there will be improvements in the rate of non-auto driver mode share ("NADMS") (i.e., the number of trips by means other than cars).  The University of Maryland studied both current NADMS conditions (approximately 30%) and the Plan's assumed NADMS (approximately 54%).  It is clear that if the Plan does not come close to achieving its NADMS goals, traffic will be a lot worse (e.g., northbound on Connecticut will be 34 minutes without improvements, but only 24 minutes if the NADMS projections are met).

  4. This analysis supports staging for at least two reasons.  First, because the models and projections are so sensitive to changes in NADMS, it is important to confirm the Plan is meeting NADMS targets before additional development should be allowed.  Second, given the total increase in development contemplated under the Plan and the 20 year duration of the Plan, there is a tremendous amount of variability and uncertainty inherent in the modelling; given how volatile the projected congestion is, it makes sense to take some interim looks as development occurs to make sure everything is proceeding in accordance with the projections.

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