This has actually been studied, and it depends on many factors like time of day + sun location, the weather, pavement conditions, and rigour during driver licensing. Optimal flow on a highway during sunshine is around 80km&#x2F;h, where the gap between the cars is around a car and a half length. Under that and we would be better off having parking lot queues before onramps.<p>So why don&#x27;t we do this? Because usually people want to travel <i>to</i> the city <i>from</i> the suburbs. The only place that has room to build these parking lots are the suburbs, but then the city couldn&#x27;t take the excess flow (since it all needs to empty out into city streets and parking lots anyway).