Cars, parking, EV charging and tolls

Much of this use case is already machine-to-machine. Chargers talk to their networks over OCPP, networks roam with each other over OCPI, cars authenticate to chargers under ISO 15118, and toll transponders work across agencies. Agents fit one layer up: the owner’s agent choosing where to charge or park within set limits, and handling the exceptions that today end in a phone call.

How it works today

EV charging. Three standards matter here:

• OCPP, from the Open Charge Alliance, connects a charging station to its charging station management system. Its releases are 1.6 (2015), 2.0.1 (2020) and 2.1 (2025), and OCPP 2.0.1 edition 3 became the international standard IEC 63584 in 2024. Version 2.1 adds ISO 15118-20 support, bidirectional charging, local cost calculation and ad hoc card and QR payment.
• OCPI, maintained by the EVRoaming Foundation, connects eMobility Service Providers (the app or card the driver uses) with Charge Point Operators, directly or through roaming hubs. Its modules cover locations, tariffs, sessions, charge detail records, tokens, remote commands and charging profiles. Version 2.3.0 is current and added optional Payment Terminal and Booking modules.
• ISO 15118 covers the car-to-charger link. ISO 15118-20, published in April 2022 with an amendment in 2026, defines the messages for power transfer in both directions. Plug and Charge uses ISO 15118 certificates to authenticate the customer, start the session and take payment with no other action at the charger.

In the US, NEVI projects and other publicly accessible chargers funded under Title 23 must meet 23 CFR Part 680. They must accept contactless debit and credit cards plus a toll-free number or SMS option, and must not require a membership (680.106(f)). They must support ISO 15118 hardware and Plug and Charge, OCPP 2.0.1 and OCPI 2.2.1 (680.108). The price must be shown in $/kWh before the session starts and cannot change during it (680.116(a)). Real-time port status and price must be available free to third-party developers by API, in OCPI 2.2.1 terms (680.116(c)). The eCFR shows no amendment to Part 680 since 30 March 2023.

Billing accuracy is a weights-and-measures matter. NIST Handbook 44 carries Section 3.40 for electric vehicle fueling systems. In Canada, Measurement Canada’s temporary dispensation program keeps billing by time or flat rate available until 31 December 2029, and participating owners must tell users how many kWh each transaction delivered.

Parking. The Alliance for Parking Data Standards, developed by IPMI, the BPA and the EPA, publishes APDS. Version 4.1 makes the API part of the standard, with resources for places, rates, right specifications, assigned rights, sessions and quotes, and webhooks for push updates.

Tolls. E-ZPass is interoperable across toll entities in 20 states. The E-ZPass Group holds no customer accounts; each member agency does. MAP-21 required Federal-aid highway toll facilities to provide electronic toll collection interoperability by 1 October 2016.

The agent-to-agent version

Illustrative. On a road trip, the owner’s vehicle agent asks a charging network’s agent for a reservation that fits the owner’s limits:

{
  "jsonrpc": "2.0",
  "id": 12,
  "method": "SendMessage",
  "params": {
    "message": {
      "role": "ROLE_USER",
      "messageId": "msg-ev-3390",
      "parts": [
        {"text": "Reserve a DC fast charger near the route waypoint for arrival between 14:10 and 14:30 local time."},
        {
          "data": {
            "near": {"lat": 45.2461, "lon": -75.9038, "radiusKm": 5},
            "arrivalWindow": {"start": "2026-10-03T18:10:00Z", "end": "2026-10-03T18:30:00Z"},
            "minPowerKw": 150,
            "maxPricePerKwh": {"amount": "0.62", "currency": "CAD"},
            "maxSessionTotal": {"amount": "45.00", "currency": "CAD"},
            "plugAndCharge": true
          },
          "mediaType": "application/json"
        }
      ]
    }
  }
}

1. The network’s agent answers from its own OCPI data: which sites fit, their current tariffs and port status, and whether its Booking module can hold a port.
2. If one fits within the limits, it confirms a reservation and returns the tariff that will apply. If not, it returns TASK_STATE_INPUT_REQUIRED with the nearest options, and the owner’s agent decides or asks the owner once the car is parked.
3. At the charger, Plug and Charge starts and pays for the session as it does today.
4. The charge detail record comes back as an artifact. If the session failed or the kWh look wrong, the owner’s agent opens a dispute on the same context.

Parking follows the same shape against an operator’s APDS rates and quotes. For tolls, the realistic agent tasks are account top-ups and disputing a plate read, with the agency that holds the account.

What has to be true

Identity. Two identities are involved. The car proves itself to the charger through the ISO 15118 certificate chain. The owner’s agent must prove to the network’s agent that it acts for that owner and that contract. Neither implies the other.

Authority. An unattended car spends money. Limits must be set in advance, because asking a driver to approve payments while driving is not acceptable. Price per kWh, a session total, networks and regions are the natural constraints. AP2’s human-not-present flow shows the pattern: the user approves open mandates with constraints, and the agent can only produce closed mandates that satisfy them.

Record. OCPI charge detail records, APDS sessions and toll transactions are the billing records today. Agent exchanges should reference them. Price shown before the session and kWh delivered are the facts most likely to be disputed, and both already have regulatory backing in the US and Canada.

Privacy. Every query carries location. Agents should send only what the provider needs to answer, such as a radius around a waypoint.

Where Emissar fits

• Mandate (spec in progress) is aimed at exactly the spending limits above, bound to the vehicle’s agent and revocable.
• Settle (planned) would check a payment against those limits and run it on AP2 or x402. Where Plug and Charge already pays, Settle has nothing to add.
• Resolve (in development) could map the brand or phone number on a parking sign to the operator’s agent endpoint.
• Ledger (spec in progress) would give both sides a signed receipt of what was quoted and agreed, useful when a charge detail record is disputed.

Open questions

• Who publishes the agent? OCPI splits the roles between the driver’s eMSP and the site’s CPO. Either could run the agent a car talks to.
• Price between quote and arrival. NEVI rules fix the price once a session starts, not when an agent asks 40 minutes earlier. Whether a reservation locks the tariff is up to the network.
• Failed sessions. Who pays for an idle reserved port, or a session that stops early, needs rules both agents can read.
• Tolls. We know of no toll agency with an A2A endpoint. Until one exists, disputes and account changes go through the agency’s own website or phone line.