The electric momentum tax: why waiting for EVs fails twice

The first failure

New sales are not the fleet on the road

Transport debates quote the share of new cars that are electric. The junction does not see new sales. It sees the whole fleet, every morning, and that fleet changes slowly. Ireland’s Central Statistics Office published its first count of the licensed fleet by fuel in July 2026.

A quarter of new sales is real progress. But cars stay on Irish roads for well over a decade, so a large share of the vehicles that will pass through a junction in 2035 are already on the road today, and most of them burn fuel. Ireland’s own target shows the gap: the Climate Action Plan aims for 845,000 private EVs by 2030. In June 2026 there were about 125,000.

Freight is further behind. Of about 443,000 goods vehicles licensed in Ireland, roughly 98% run on diesel and about 1.3% are electric. A heavy goods vehicle loses many times a car’s energy at every forced stop, so the vehicles that waste the most are the ones that will electrify last.

Waiting for the fleet to turn over means another generation of stop-start fuel burn at every set of lights.

The second failure

An electric fleet still pays the tax

Now jump to the day every vehicle is electric. The momentum tax shrinks, but it does not disappear, because it is set by physics, not by the tailpipe. A moving car carries kinetic energy in proportion to its mass and the square of its speed. A red light takes that energy to zero, and the car has to buy it all back from rest.

Regenerative braking is a genuine improvement on brake discs. But to be reused, the energy has to make two journeys, and it loses some on each. Then whatever is lost has to be replaced from a power station, a wind farm or a solar panel. That is the full well-to-wheel account of a stop.

1. Coasting on the approachEnergy spent pushing through air and tyre resistance as the car slows still moves it forward, so it is not lost. A driver who lifts off early lets more of the stop happen this way.
2. Wheel to battery, as the car stopsGearbox, motor working as a generator, inverter and battery charging each take a share. Below walking pace the friction brakes finish the stop, a small loss. On a typical stop about 57% of the motion energy reaches the battery.
3. Conditions that limit itA battery near full cannot accept much charge, so regeneration is cut after a top-up. A cold battery accepts less. A hard stop exceeds what the motor can absorb, and the discs take the rest. On a wet or icy road, stability control limits it again.
4. Battery to wheel, as it pulls awayThe same chain runs in reverse: battery, inverter, motor, gearbox. About 82% of what was stored reaches the wheels again.
5. While it waitsHeating, cooling and the car’s electronics keep drawing power for every second at the red light. On a winter morning that can equal a large share of the stop’s motion energy.
6. Well to battery, to replace itEvery unit lost has to be generated, carried through the grid and charged back into the battery, with losses at each step.

That last figure is the strongest. Regeneration can win back some of the energy. Nothing wins back the time: an electric car waits in the same queue, for the same light, as the diesel beside it.

Test it yourself

Does regeneration fix it?

Even the best case, an early, gentle stop with a warm, half-full battery on a mild day, loses around a quarter of the motion energy, and takes more again from the source to put it back. Clean electricity is not free electricity.

Side by side

Diesel today, electric tomorrow, free flow either way

The grid

Stop turning clean megawatts into brake heat

Ireland’s grid is already under strain. Data centres used 7,663 GWh in 2025, 23% of all metered electricity, up from 5% in 2015. In December 2025 the Commission for Regulation of Utilities set new connection rules for data centres: larger sites must bring their own dispatchable generation or storage, and data centres above a minimum size must source at least 80% of their annual demand from new Irish renewables.

Electrifying the fleet adds a second large load to that grid. If those vehicles still stop at every set of lights, part of every charge is generated, transmitted and stored only to be lost at the stop line, and much of it is put back during the evening peak.

Umpireal removes the stop, whatever the vehicle runs on. Traffic keeps its momentum on the elevated road, and people walk and cycle through an open, daylit underpass, well lit and covered by CCTV at night. Within the road structure, the Innerspace houses 1 MW of AI compute and 4 MWh of battery storage on a 350 m² footprint, so the node brings its own storage to the grid from day one, and the compute pays for the junction.

The fleet will change its fuel. The physics of the stop will not change, and neither will the wait. Only the junction can.

Sources

Where the figures come from