This report contains the findings of a special speed study conducted by the Massachusetts Department of Public Works --- Traffic Engineering Section to determine trends in traffic operating speeds on State Highways.

The primary purpose of the survey was to confirm or disprove an often stated argument that regardless of the existing posted speeds the motor vehicle operator chooses an operating speed that he considers to be reasonable and prudent for the existing conditions.

Two State Highways were selected that were considered to be typical of those within the State Highway network. Route 128 in Beverly, a circumferential expressway with a medium high traffic volume and Route 114, a two lane highway through the municipalities of Peabody, Danvers, and Middleton, a secondary type highway with a medium traffic volume.

Radar speed meters were used to record the speeds of the various vehicles that passed through the nineteen stations on Route 114 and the six stations on Route 128.

Initial observations were taken under non-peak hour conditions and the 85th percentile speeds were determined. Existing speed limit signs were then substituted by signs with numerical limits of ten (10) miles per hour lower and ten (10) miles per hour higher and another set of radar speed observations with resultant 85 percentile speeds were taken one day after and one week after the substitute signs were erected for comparison with the initial observations.

As a result of over 16,000 observations recorded, there was an increase in the average speed of 0.41 miles per hour or 3/4 of one (1) percent (0.0076) from the initial observations. This minor increase is the obvious result of testing techniques, equipment (speed meter), operator error, and chance variance and can, therefore, be entirely discounted.

The 85th percentile speed used as a basis for this study is the speed at or below which 85 percent of the observed vehicles travel. It is a principle that is accepted nationwide that posted speed limits should be close to the 85th percentile speed.

Therefore, it is concluded from this special speed study that traffic consistently ignores posted speed limits and runs at speeds which the drivers consider reasonable, convenient, and safe under existing conditions. The experiment further demonstrated that the posting of unrealistic speed signs that are lower than the maximum allowable safe speed is unfair to the road user, is not consistent with the design and construction of the roadway, fosters a disregard for all regulatory signs and serves only to satisfy emotion.

Special Speed Study

City/Town	Station	Existing Posted Speeds	85th percentile speed
			Existing Posted Speeds	10 MPH Lower Posting		10 MPH Higher Posting
				1 Day	1 Week	1 Day	1 Week
Route 114 Northbound
Peabody	63+00	35	40	42	40	40	42
	40+00	35	44	48	48	48	46
	18+00	35	46	48	48	48	48
Danvers	119+00	40	50	50	48	48	50
	85+00	40	48	50	50	50	48
	43+00	45	50	50	50	52	50
	6+00	45	52	52	54	54	54
Middleton	230+00	45	50	50	50	50	52
	199+00	40	44	48	48	48	50
	156+00	30	44	42	52	52	52
Route 114 Northbound
Peabody	61+00	35	42	42	44	40	40
	40+00	35	42	42	44	42	42
	15+00	35	48	48	50	50	50
Danvers	121+00	40	52	50	50	50	50
	83+00	40	50	50	50	50	50
	42+00	45	50	52	54	52	50
	10+00	45	50	50	50	50	48
Middleton	196+00	40	48	50	48	52	48
	227+00	40	52	52	50	50	52
Route 128 Southbound
Beverly	220+00	55	62	62	62	64	62
	110+00	55	60	60	60	60	60
	79+00	50	60	60	60	60	62
Route 128 Northbound
Beverly	75+00	50	60	60	60	60	60
	110+00	50	60	60	60	60	60
	220+00	55	62	62	60	64	62