No, there's no a priori reason why public transport should be slower. There are cities where it isn't the case, London for example.
Cars get stuck in traffic (because they are traffic). Trains don't, and can reach higher speeds. Buses have (or should have) their own lanes, and priority at traffic lights, so that they don't get stuck behind cars. A single bus lane can have more passenger throughput than several car lanes; it's an absurdity that a bus should be delayed by single-occupancy vehicles hogging the space.
If public transport is slower than driving, your city is doing it wrong.
There is. You have to get to and from the station / stop twice every trip. This makes it slower unless you are in an area where the density is so high that the space constraints make cars prohibitive.
>You have to get to and from the station / stop twice every trip.
And you have to get to and from your parking spot.
>an area where the density is so high that the space constraints make cars prohibitive.
Yes, these areas are called "cities".
---
There are a lot of factors that go into determining the relative speeds of public transport vs private motor vehicles. Here are some of them (for buses):
- street network topology: grid, spaghetti, cul-de-sacs?
- are there highways slicing through the city, or is it mostly smaller roads?
- speed limits on those roads
- is there a congestion charge?
- are there dedicated bus lanes?
- is there priority for buses at intersections?
- spacing of stops
- boarding, payment, disembarking procedure
- frequency of rides
- directness of the route
- viability of other non-car transport modes e.g. cycling
Different answers to these questions give different journey times. Whether transit is faster than driving is the net result of all these questions. And most of them are political in nature. It's a choice, not some iron law.
Plus, there's the obvious existence proof of fast public transit: airlines.
Cars get stuck in traffic (because they are traffic). Trains don't, and can reach higher speeds. Buses have (or should have) their own lanes, and priority at traffic lights, so that they don't get stuck behind cars. A single bus lane can have more passenger throughput than several car lanes; it's an absurdity that a bus should be delayed by single-occupancy vehicles hogging the space.
If public transport is slower than driving, your city is doing it wrong.