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342-7
Table 342-6. DESIGN SPEEDS (BY ROADWAY TYPES)
Highway Type Design Speed, km/h (mph)
Inter,t,ile Rural 105(65)
Rural Highways 90(55)
Flat Terrain 90(55)
Rolling Terrain 80 -90(50-55)
Rough Terrain 50 -80(30-50)
Urban Interstate
Through Areas of Concentrated Development 80(50) minimum
Through Areas of Moderate Development 65 -90(40-55)
Urban Expressways 65 (40) minimum
Through Areas of Concentrated Development 5000) minimum
Through Areas of Moderate Development 50 - 80 (30 - 50)
Minor Residential Streets 40(25)
Access Roads - Recreational Development 25 - 40 (15 - 25)
Drives - Site Access Roads 15 - 30 (10 - 20)
Note : The selection of the design speed should be done with great care on the premise that once selected, all pertinent geomet-
ric design should be related to the value selected.
sight/stopping distances in Table 342-7 Second, trucks often travel more slowly
assume a braking distance on a level road- than passenger vehicles .
way. If the vehicle is traveling uphill, the
braking distance is decreased . Conversely, if Passing Sight Distance:
the vehicle is traveling downhill, the brak- It is often necessary on two-lane roads to
ing distance is increased . When a highway provide an opportunity to pass slow mov-
is on a grade, the braking distance is ing vehicles . Table 342-8 gives the mini-
expressed by the formula : mum passing sight distance .
v2 Figure 342-7. Classification of circu-
d = 3 .0 ROADWAY
30 (f±G) DESIGN lar curves .
ELEMENTS
where G = grade of the road (uphill
grades are +, downhill 3 .1 Horizontal ponents of Horizontal Alignment:
grades are -)
General Design Criteria for Horizontal Horizontal alignment is -
Alignment: posed of two ponents (see
Figure 342-7) :
Example: Given that V = 40 mph and In addition to the design controls
specific 1 . Straight lines (tangents) .
that G =-10%, described in 2 .0 of this section, a number of
2 . Circular curves (arcs).