Street circuits put a race into a city center instead of a purpose-built facility. Everything about the event, including the shape of the track, follows from working around a functioning city.
The surface was not built for racing
Public roads are laid for ordinary traffic, with drainage cambers, manhole covers, painted markings and joins between resurfacing sections that behave unpredictably at racing speed.
Organizers resurface sections, weld down covers and grind problem areas, but the road remains a compromise rather than a purpose-built surface.
Grip is typically low at the start of a weekend and improves as rubber is laid down, which is why lap times fall more across a street weekend than at a permanent circuit.
Walls replace runoff
Permanent circuits use gravel traps and asphalt runoff to slow a car that leaves the track. A street layout has buildings and sidewalks where that space would be.
Barriers therefore sit close to the racing line, which means a small mistake ends a race rather than costing a few seconds.
This changes driving and strategy. Drivers build up to the limit more cautiously, and teams plan for a higher probability of safety car periods than at a permanent venue.
Construction happens around normal life
Barriers, fencing, grandstands and pit facilities are temporary structures assembled over weeks and removed afterward, largely at night to limit disruption.
Roads close in stages, and cities negotiate the schedule carefully because the same streets carry commuters, deliveries and residents throughout the build.
The cost of that build is a large part of why street races are expensive to host, and it recurs every year rather than being a one-time facility investment.
Layouts are dictated by geography
Designers cannot choose corner sequences freely. The track follows existing roads, and its character comes from whatever the street grid happens to provide.
Cities laid out in blocks produce sequences of slow ninety-degree corners, which limits overtaking because cars cannot follow closely through them.
Designers compensate with long straights into heavy braking zones, since that is the one overtaking opportunity a grid layout reliably offers.
The event is partly a civic product
Host cities justify the disruption on tourism and visibility rather than on ticket revenue alone, treating the broadcast images of the city as part of the return.
That reasoning explains why circuits are routed past recognizable landmarks even when a less scenic layout would produce better racing.
It also explains the surrounding programming of concerts and hospitality, which broadens the paying audience beyond people who came specifically for the cars.