California offers two main FasTrak transponder types: the Standard tag, for drivers who always pay full toll, and the Flex tag, which has a sliding switch so carpoolers can claim discounted or free travel in express lanes. Two specialty sticker versions cover motorcycles and vehicles with metallic windshields that block signal. Which one you need comes down to one question: do you ever drive an express lane with passengers?
The Standard Transponder
The Standard tag comes in two forms. One is a thin sticker that adheres to the windshield. The other is a hard-case device that mounts near the rearview mirror with adhesive strips and includes a battery that may beep when read by roadside equipment. Both transmit your account information to overhead sensors, and the toll is debited from your prepaid balance.1The Toll Roads. Types of FasTrak Transponders
The limitation is simple. A Standard tag has no way to tell the system how many people are in the car, so you always pay the full posted toll. On Bay Area bridges that does not matter, because the toll is flat. On express lanes it means you forfeit any carpool discount, even with a full car.2FasTrak. Carpooling Guide
So the Standard tag fits you if your driving stays on toll bridges, or if you only ever use express lanes alone. The hard-case version has a practical bonus: you can peel it off one windshield and move it to another vehicle.3FasTrak. FasTrak Throughout California
The FasTrak Flex Transponder
The Flex is a hard-case transponder with a three-position switch on its face. Before you drive, you slide it to match the number of occupants: position 1 for solo, position 2 for two people, or position 3+ for three or more. Overhead equipment reads that setting along with your account data and applies the right toll.3FasTrak. FasTrak Throughout California
On bridges, the Flex works exactly like a Standard tag no matter where the switch sits. Its value is in express lanes, where carpools qualify for reduced or free tolls. If you ever ride express lanes with passengers, the Flex is the only tag that opens up those discounts.2FasTrak. Carpooling Guide
Set the switch honestly. If enforcement cameras find that your declared occupancy does not match the actual number of people in the car, you can receive a toll evasion notice. The first notice adds a $10 penalty on top of the unpaid toll, and a second jumps to $30.4C/CAG. Schedule of Penalties for Toll Evasion Violations
How to Choose Between Standard and Flex
The deciding factor is the occupancy rule on the express lane you use. Those rules vary, and setting the switch wrong (or using a Standard tag) will cost you the discount.
In the Bay Area:
- Two-person carpool lanes (I-580, I-680): a Flex on position 2 or 3+ rides toll-free.
- Three-person carpool lanes (SR-237, I-80, I-880, US-101, US-101/SR-85): three or more occupants on position 3+ ride free, two occupants on position 2 get 50% off, and solo drivers on position 1 pay the full dynamic toll.
A Flex set to position 1 or any Standard tag always pays the full express lane toll, regardless of who is actually in the car.2FasTrak. Carpooling Guide
Express lanes in Los Angeles, Orange County, San Diego, and the Inland Empire each set their own thresholds. Before using a new corridor, check the operating agency’s rules so you know whether two or three occupants trigger the discount. The practical takeaway: when in doubt, order a Flex. It behaves as a Standard tag when you want it to, and it is the only tag that gives you the option to claim a carpool rate later.
Specialty Stickers for Motorcycles and Metallic Windshields
Two additional form factors exist for vehicles that cannot use a windshield-mounted tag:
- A headlamp sticker transponder, for vehicles whose windshields have a metallic coating that blocks signal. It adheres to the headlamp lens.
- A motorcycle sticker transponder, which mounts on a motorcycle’s headlamp lens or cover.
Both work like a Standard tag and cannot communicate occupancy. Motorcycles are treated as carpools on most express lanes and ride toll-free, provided the rider has a Flex tag set to the appropriate position.1The Toll Roads. Types of FasTrak Transponders
What Happened to the CAV Tag
California used to offer a FasTrak CAV (Clean Air Vehicle) transponder that let drivers of qualifying zero-emission and plug-in hybrid vehicles with a DMV decal use carpool lanes and receive express lane discounts while driving alone. That program is over. The DMV stopped accepting new CAV decal applications on August 29, 2025, and all existing decals became invalid on October 1, 2025. Clean air vehicles now follow the same occupancy rules as any other car.5California Department of Motor Vehicles. Clean Air Vehicle Decals
If you already have a CAV transponder, you do not need to replace it. FasTrak automatically converted all CAV tags into standard Flex transponders, so yours now works as a regular Flex with the three-position switch.6FasTrak. Clean Air Vehicle Discounts Being Discontinued
The No-Transponder Alternative
If you only cross Bay Area toll bridges and never touch an express lane, you can skip the hardware with a License Plate Account. Your plate is linked to your FasTrak account and bridge cameras read it. Two versions exist: a long-term account for regular commuters, and a short-term account covering a 48-hour window or up to 30 days in advance.7FasTrak. License Plate Account
The catch: a License Plate Account cannot be used on express lanes and does not qualify for carpool discounts on bridges. If you want either, you need a physical transponder.
What a Transponder Costs
Each transponder requires a $25 prepaid starting balance to cover tolls. FasTrak also charges a $5 refundable security deposit per tag, waived for up to three tags on accounts set up with automatic replenishment. Additional tags beyond three still carry the $5 deposit.8Bay Area FasTrak. Get FasTrak There is no monthly maintenance fee on transponder accounts.9The Toll Roads. Do FasTrak Accounts Have Account Maintenance Fees? The hardware itself costs the same whether you choose a Standard sticker, a Standard hard-case, or a Flex, so paying extra for flexibility you may use later is not really a factor.