Exit Number - Sequential Numbers

Sequential Numbers

The first exit numbers were sequential. This type of exit numbers usually begins with exit 1 at the beginning of the road; each subsequent exit is given the next number. In the case of cloverleaf interchanges, where two sets of ramps connect two roads, the separate exit ramps are often suffixed with a letter, such as 15A and 15B. Some older schemes assigned directional letters (15N for northbound, 15S for southbound) In France and Japan, decimals are used, as in 15.1 and 15.2.

When new exits are added to a road between two existing exits, the new exit is often given a number with a letter suffix, for example exit 15A may be assigned to a new exit between exit 15 and exit 16. On the New York State Thruway, an exit was added between 21 and 21A, leading to the sequence 21 - 21B - 21A - 22. In Florida, some new exits got the suffix C, so that if it had or acquired separate exits for the two directions they would be 15CA and 15CB rather than 15AA and 15AB, and also if the original exit with the same number got separate ramps per direction they would be (for example) 15A and 15B instead of having to renumber the new interchange.

Occasionally sequential exits are renumbered due to added exits. For instance, the Hutchinson River Parkway in New York was renumbered so that its northernmost exit, 27, became 30. However, the Merritt Parkway, which continued its exit numbers in Connecticut, was not renumbered, and the sequence now jumps from 30 down to 27 (the interchange on the state line had two exit 27s, and now has exits 30 and 27).

The Atlantic City-Brigantine Connector in Atlantic City, New Jersey approached the previous problem in a different way by using letters without numbers for its exits. The connector was appended to the eastern end of the Atlantic City Expressway, thus extending the highway from mile zero. Assigning the connector numbered exits would have required re-numbering all the exits on the entire expressway.

Eleven U.S. states currently use sequential numbering schemes, although amendments to the Manual on Uniform Traffic Control Devices require them to transition to distance-based numbering.