Frequent access connections, median openings, and closely spaced traffic signals are a recipe for congestion on major roadways (See Figure 1-3). Studies of the effects of access management on roadway operations have addressed effects of access spacing on travel time by simulating traffic performance. Collectively, these studies indicate that access management helps to maintain desired speed and reduce delays, which also reduces fuel consumption and vehicle emissions.

For example, analysis based on procedures in the Highway Capacity Manual indicates that the typical reduction in free-flow speed (for one direction) is approximately 0.15 mph per access point and 0.005 mph per right-turning movement per hour per mile of road.¹ Using the Highway Capacity Manual, Table 1-2 provides suggested access density adjustment factors for level of service determinations. These benefits extend not only to free-flow conditions, but to platoon flow as well.

Table 1-2: Access Points and Free Flow Speed

Access Points and Free Flow Speed
Access points per mile	Reduction in free flow speed, mph
0	0.0
10	2.5
20	5.0
30	7.5
40 or more	10

Other analyses suggest that a four lane divided major roadway with long, uniform signal spacing, directional openings between signals, and auxiliary lanes could accommodate a similar volume and similar quality of service as a six lane divided roadway having traffic signals at ¼-mile intervals, unregulated access between the signals, and no auxiliary lanes.²

Minimizing the number of traffic signals and promoting appropriate signal spacing significantly improves travel times. Each traffic signal per mile added to a roadway reduces through travel speed about two to three mph. Table 1-3 indicates percentage increases in travel times that can be expected as signal density increases, using two traffic signals per mile as a base. For example, travel time on a segment with four signals per mile is about 16 percent greater than on a segment with two signals per mile.

Table 1-3: Travel Time and Signal Density

Percentage Increase in Travel Times as Signalized Density Increases
Signals Per Mile	Percent Increase in Travel Times (Compared with 2 Signals Per Mile)
2.0	0
3.0	9
4.0	16
5.0	23
6.0	29
7.0	34
8.0	39