Walk into any dealership and you'll find vehicles capable of speeds that would guarantee prosecution if attempted on public roads. A modest Toyota Corolla tops out around 140mph. A Ford Fiesta manages 120mph. Even commercial vans exceed legal limits by considerable margins. Given that the highest speed limit in America is 85mph and Britain's motorways cap at 70mph, the question seems reasonable: why build cars this fast at all?
The engineering answer centers on what happens when you don't. A vehicle designed to barely reach the speed limit would spend its entire motorway existence at or near redline, the maximum safe engine speed. That constant strain destroys reliability, increases maintenance costs, and makes for miserable fuel economy. By contrast, a car capable of 150mph cruises at 70mph using perhaps 2,000 RPM, operating well within its comfort zone with minimal mechanical stress.
This principle of overengineering underpins modern automotive design. Manufacturers want vehicles that can maintain highway speeds reliably for decades. The solution involves creating powertrains capable of far higher performance than daily driving demands. At motorway speeds, these engines barely break a sweat, which translates directly into longevity and reduced running costs.
Transmission design reinforces this approach. Creating seamless shifts through the gearbox requires headroom beyond legal speeds. If top speed matched the speed limit exactly, gearing ratios would force the engine into inefficient operating ranges during normal driving. You'd hear it screaming at 4,000 or 5,000 RPM just to maintain 70mph. Modern transmissions allow comfortable cruising at low engine speeds precisely because they're engineered for much higher velocity.
The acceleration question deserves consideration too. Vehicles need substantial power reserves for overtaking maneuvers, particularly on two lane roads with oncoming traffic. The ability to accelerate briskly from 60mph to 80mph reduces time spent in the opposing lane, directly improving safety. A car struggling to reach its maximum speed lacks the power for these essential maneuvers.
International markets complicate any attempt at universal speed restrictions. Germany's Autobahn famously has no speed limit on many sections, and manufacturers design vehicles for global sale. Artificially limiting American market cars while leaving European versions unrestricted would require separate engineering programs, increasing costs without meaningful benefit. The automotive industry operates on economies of scale that make such regional variations impractical.
Safety equipment rated for high speeds provides benefits at lower velocities too. Braking systems, suspension components, and tire specifications designed for 150mph operation handle 70mph with considerable margin. The same principle applies to chassis rigidity and aerodynamic stability. A vehicle engineered to remain composed at triple digit speeds feels planted and secure at legal limits.
Market forces play their role as well. Consumers associate higher performance with quality engineering and prestige, even if they never approach maximum velocity. The specifications sheet matters for resale value and brand positioning. Two otherwise identical vehicles with different top speeds command different prices, regardless of how buyers actually use them.
The emergency argument surfaces occasionally, though it carries less weight than other justifications. Rushing someone to hospital or fleeing immediate danger might theoretically require excessive speed, but these scenarios remain rare enough that they can't justify design decisions affecting millions of vehicles.
Political and practical realities make universal speed limiting impossible anyway. Different road types demand different capabilities. A delivery van needs power for motorway merging that would be excessive for residential streets. Standardizing restrictions across vehicle types, road classifications, and international markets presents insurmountable complications.
Perhaps the simplest explanation is that limiting top speed doesn't actually limit the speed people drive. Electronic limiters are easily defeated or removed. The meaningful constraint comes from enforcement, not mechanical capability. Building cars that physically cannot exceed 70mph wouldn't stop speeding. It would just produce worse vehicles that struggle with everyday driving tasks while annoying consumers and accomplishing nothing meaningful for road safety.
The excess speed capability in modern cars represents thoughtful engineering rather than irresponsible design. Those unused MPH make vehicles more reliable, efficient, and capable where it actually matters: navigating daily traffic safely and comfortably within legal limits.
