Cleaner air, without penalising the ambulance

A clean air zone only works if the charge is applied consistently and the exemptions are honoured without exception. Charging someone travelling to an emergency medical facility is not a billing error — it is a policy failure with a human cost.

The system also had to serve residents who are not sitting at a desk. Access had to work from a phone, at the roadside, without a support call.

We built the platform on a microservices architecture so that user management, voucher issue, payments and notifications scale and change independently of each other.

An API gateway fronts every client request, handling routing, authentication and rate limiting so that the web app and both mobile apps talk to the same governed surface. Exemptions for medical visits are handled inside the voucher service itself, as a first-class rule rather than a manual correction after the fact.

• Microservices User management, vouchers, payments and notifications deploy and scale independently.
• API gateway One entry point for every client, with routing, authentication and rate limiting applied consistently.
• Medical exemptions Hospital and emergency journeys are exempted by rule inside the voucher service, not by manual correction.
• Three channels A responsive web application plus native Android and iOS apps, all on the same API.

A responsive UI layer and mobile apps sit behind an API gateway, which routes to independent services for user management, voucher lifecycle and payments — so a change to charging logic never risks the registration path.

Residents register, apply for a voucher and check its status from whichever channel suits them, and exemptions are applied by policy rather than by exception handling.

The service boundaries mean the charging rules can be changed as air-quality policy changes, without a rebuild.