Passing sight distance for two-lane, two-way highways per the AASHTO Green Book, and a check of whether the sight distance available permits passing or a no-passing zone must be marked.
The current Green Book passing sight distances are consistent with the MUTCD no-passing zone warrants and field observations of passing on two-lane highways. Where the sight distance available is less than the value required, a no-passing zone should be marked. These are the values to use for design and for marking passing and no-passing zones.
highlighted = current selection.
Passing sight distance applies to two-lane, two-way highways, where drivers overtake slower vehicles using the opposing lane. It is not needed on multilane or divided roads. It governs the marking of passing and no-passing zones and is checked on crest vertical curves and horizontal curves, where the view of oncoming traffic is limited. Where passing sight distance cannot be provided often enough, consider passing lanes or climbing lanes to maintain safety and level of service.
It is the sight distance a driver on a two-lane, two-way highway needs to pass a slower vehicle safely using the opposing lane, without conflicting with an oncoming vehicle. It is measured from a 1.08 m eye height to a 1.08 m high oncoming vehicle.
Where the sight distance available on the section is less than the passing sight distance for the design speed, a no-passing zone should be marked. Enter the measured sight distance on the first tab to check.
The design values follow A Policy on Geometric Design of Highways and Streets, 7th Edition (2018), consistent with the MUTCD no-passing zone warrants. Always confirm against the edition adopted by your road authority.