Gap Acceptance

1
Gap Acceptance
Sight Triangles
Clear Sight Triangle
Clear Sight Triangle
A Approach Sight Triangles
Clear Sight Triangle
Clear Sight Triangle
B Departure Sight Triangles
2
Intersection Sight Distance
94 GB 90 GB
2001 GB
Speed
ISD
ISD
80 km/h
250 m
170 m
50 mph
840 ft
555 ft
ISD intersection sight distance for
turning left from stop onto major highway
3
Offset Left - Turn Lanes
Advantages

• Better visibility
• Reduced conflict
• More vehicles served

Parallel
Tapered
4
Miscellaneous

• Horizontal control see Chapter 3
• Deceleration length
• Discussion revised
• Additional design speeds and values included
• Discussion on driveways expanded

5
Chapter 10 Grade Separations and Interchanges
Access separations and control on
crossroad at interchanges
Turning roadway widths Single - point urban
interchanges Superelevation and cross
slopes Two lane entrance ramps
6
Miscellaneous

• Recommends separation of bicycle/pedestrian
  movement from vehicle movement through
  interchanges
• Single Point Urban Interchange discussed as
  separate type
• Exhibit 10-67 made consistent with Exhibit
  3-55

7
Access Control at Interchanges
Minimizes spillback on ramp crossroad Distance
for crossroad weaves Distance for merging
maneuvers Provides storage for turning vehicles
8
Miscellaneous

• Cautions against the use of minimum values
  for taper type entrances
• Exhibit 10-70 Acceleration lengths have been
  recomputed
• Adds a caution concerning volumes exceeding lane
  capacity on 2-lane ramps

9
Technical Corrections

• Exhibit 3 - 55 and Exhibit 10 - 67 - In
  metric side, under Case I column, replace
  with with no so it is identical with
  US Customary.
• Exhibit 3 - 76 - Delete and Sag from
  title.
• Exhibit 5 11 - Replace 5.5 under
  residential in the metric side with 2.2.

10
Technical Corrections

• Exhibit 10 - 60 is incorrect. It should be
  similar to Figure IX-66 in 94 GB.
• Exhibit 10-71 - In the metric side under
  the column All Speeds, change 3 to 4
  Downgrade to 5 to 6 Downgrade

11
Future Research
Truck impacts on criteria ( underway
) Improved design for freeway speed change
lanes ( proposed ) Design criteria and
warrants for right turn deceleration (
proposed ) Auxiliary through lanes and lane
drops ( proposed ) Passing sight distance (
proposed )