Civil Engineering Reference
In-Depth Information
Table 7.5 Estimated speeds from inclement weather
Precipitation condition
Observed speeds (MPH)
Ratio to no precipitation
No precipitation
64
1
Drizzle
51
0.8
Light rain
50
0.8
Light snow
45
0.7
Rain
48
0.8
Sleet
37
0.6
Snow
37
0.6
Thunder showers
53
0.8
Thunder storm
47
0.7
Strong thunder storm
28
0.5
Source
Reference [
10
]. With permission from ASCE.
7.3.1.2 Surge in Demand
Surges in traf
c demand include sports events, seasonal shopping, cultural and
recreational events, etc. Vehicle traf
c demand in excess of roadway capacity
creates queues resulting in lower traf
c speeds. Delay lasts longer than the duration
of the demand surge.
7.3.1.3 Inclement Weather
Bad Weather: rain and snow reduce visibility and causes drivers to reduce speed.
The presence of snow and ice on the road can also reduce speeds. Advances in
sensor technologies and continued deployment of intelligent transportation system
(ITS) architectures provide the means to anticipate, mitigate, and intervene through
various traveler advisory and control measures to better manage traf
flow in
periods of inclement weather [
9
]. Light rain could reduce freeway speeds by 20 %;
while severe thunder storms could create a speed reduction of about 50 %
(Table
7.5
).
The effect of pavement conditions from weather events on traf
c
fl
c speed is
summarized in Table
7.6
.
7.3.1.4 Work Zones/Street Closures
Road Repair
: Construction activities on roadways result in physical changes to the
roadway including: narrower lanes, lane shifts, reduction in the number of travel
lanes. In addition, slower speed limits are also established in construction zones.
These changes increase travel time.
