City planners don't design roads

City planners don't design roads. Traffic engineers do, and they explicitly follow geometric design manuals produced by a clubbish non-profit named AASHTO (American Association of State Highway and Transportation Officials), whose rules are then adopted by FHWA, which then makes them a requirement for local DOTs, who then make them a requirement for cities and counties. And even in cases when places are not required to use the AASHTO standards (non-federally funded roads), traffic engineer (mis)-apply the standards because they don't have anything better. 

This is despite the fact that most roads mileage is not, in fact, Federally funded. The vast majority of roads, by functional class, are local roads in subdivisions, the design of which is governed by local subdivision ordinances, which are the province of standards set by local engineers. The total thought that goes into them consists of two concerns: 1) "They should be wide enough for two cars to pass, even with people parked on both sides", and 2) "They should be good enough to last a long time without the city needing to rebuild them". Fire marshal concerns about fire access - routes to get to houses from a fire station being too long or circuitous -- also influence design. City planning only gets involved when a city has had issues with too curb cuts onto highways, or traffic lights too close together. It's fair to blame city planners for every land use problem, but city planners have remarkably little to do with roads.