ARTERIAL ROADWAYS:
Comparison between 1996–1999 Speeds Data and
2001–2003 Speeds Data

We present a comparison of the travel speed index for monitored roadways from the 1996–1999 CMS data collection and from the 2001–2003 monitoring period, for both the morning and evening peak periods. Only roadways common to the two monitoring periods are included in this comparison. All of these roadways in this comparison are classified as Class III urban arterial roadways.

Change in Travel Speeds
Average observed travel speeds on arterial roadways in the morning peak period appear to have decreased in the most recent data-collection years. In general, the percent of roadway miles with traffic traveling at average travel speeds greater than 30 mph has decreased between the two monitoring periods, while the percent of roads with average speeds at 18 mph or less increased. The percent of roads with average speeds at 18 mph or less increased by 3 percent regionwide, and 4 percent fewer roads now have average travel speeds greater than 30 mph.

For the 2001–2003 data collection period, 8 percent of the roadways in the subregion made up of Boston and its inner suburbs had average observed morning-peak-period speeds of 14 mph or less, an increase of 4 percent from the 1996–1999 period. The data indicate that this subregion also experienced a decrease between the two periods in the percent of arterial roadways with average travel speeds greater than 30 mph; the decrease was from 40 percent to 33 percent. However, looking at the monitored roadways in the region as a whole, or at the roadways in the outer suburbs subregion, the trend of declining speeds in the morning peak period is not as pronounced.

In the evening peak period, the average speeds do not seem to have significantly changed since the earlier data collection period. The percent of roads with average speeds of 18 mph or less increased from 7 percent to 10 percent regionwide. Approximately 24 percent of the monitored arterial roadway segments in the subregion made up of Boston and its inner suburbs had an average observed travel speed of 18 mph or less in the evening, according to 2001–2003 data, compared to 20 percent of the roadways in the earlier data collection period. Similarly, an increase from 5 percent to 8 percent is observed between the two monitoring periods for the roadways in the outer suburbs.

The data show that there was a decrease in free-flow speeds in both peak periods for roadways in the MPO region, based on the speed index measure. The roadways in the subregion defined by Boston and its inner suburbs appear to have had the largest decrease in free-flow speeds, particularly in the morning: 51 percent of roadways in 1996–1999 had traffic traveling near or above the speed limit on average, compared to 39 percent in 2001–2003.

As would be expected, the data also show an increase in the percent of roadways with traffic traveling below 70 percent of the speed limit, in both peak periods. All areas of the MPO region exhibit this increase in slower travel.

The changes in both the free-flow and congested speed index categories are more evident in the morning peak period than in the evening.

Speed Index on Arterial Roadways (Urban Street Class III) in the Morning Peak Period:
A Comparison between 1996–1999 Data and 2001–2003 Data