Abstract
Thia paper is hased on the wave theory Put forward by highthillland IJhitham (1955) and is concerned witli the braking; of a flowof motor cars ae a re sult of a shock wave xvhich, at the begin-ninl! of the read period, moves Erom the stp lino hackwardsalom; the rond apainat the incomi.ng traffic, reducinl; the epeet'iof the Jatter, It is sul!gested that the longah of the queueshould be de.fined hy that Part of the incoming traffic whichis affected by the shock waves. On t.hia basis, a method iaproposed for determininl! the l.ength of thP approach lanenrerltti red.