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The system was made by Amtech but was replaced in 2008 by a new system made by CS Eng. To use the system, drivers must place a transponder unit (Tag) on their windscreen to identify their vehicle as they drive through the toll lane. Lanes through the toll booths are dedicated as either Tag (unstaffed), cash (staffed) or automatic debit/credit card only (Coinbins have been withdrawn). The new tags are significantly larger than the older units, and the vehicle needs to proceed further toward the barrier before they operate due to the limited area in which the reader "reads" the tag. This prevents the complication of the old system where another tag user could enter the yellow box marking behind the user at the barrier and operate the system with their tag which would then cause the barrier to stay down for the user that entered the boxed area and thus "paying" for the user in front to cross.
Severn TAG types
There are three types of Severn TAG 
- Season Tag This type of tag allows the user to purchase a set period of time in which you can cross an unlimited amount of times, the tag may only be used on one vehicle and is not transferable between vehicles. A saving can be made if the user makes more than 17 journeys per month in a class 1 vehicle (car) when using this type of Tag. There are different levels of payment for different classes of vehicle.
- Trip Tag This type of tag is a pay-per-journey tag, useful if the user intends to make fewer than 17 journeys per month with a class 1 vehicle (car). Credit is added to an account each month by Direct Debit cheque BACS or Online via the Severn Bridge website. When the user passes through the toll, the amount of the toll is deducted from the account. An indication at each toll lane informs the user that their account credit is low. If there is no money in the account then the Tag is declined and the user must have to pay with cash. The trip tag is transferable between vehicles of the same class, i.e. between two cars but not a car and a truck which would evade paying for the correct type of vehicle.
- Car Pool or Shared Tag This type of tag allows between 2-5 cars to share one tag account. The users are able to obtain 1 tag and then use it amongst themselves to share the toll, the price of that tag is the same as a season tag however, it can be used on up to 5 vehicles, and can be temporarily moved to another vehicle within the same class. The tag can only be used by 1 vehicle in any 24 hour period, but that vehicle can pass as many times as it chooses.
All types of Tag require a £30 Deposit. If the tag is lost or stolen, a new one is issued after payment of another £30 deposit.
Limitations and drawbacks
- The Season TAG can only be used with one registered vehicle, this prevents misuse, however it complicates matters for two car families, users who regularly change vehicles or those who have courtesy vehicles etc. This is judged a misuse which can result in a Severn River Crossing "Fine" of £25+VAT.
- There is no discount for Trip Tag users, and therefore little incentive to use it other than convenience.
- Non Tag users inadvertently drive into Tag-only lanes and block the lane. At the Second Severn Crossing with a dedicated "high speed" Tag lane, this will cause a large queue to build up quickly, whilst an attendant is called to deal with the violator.
- The new tags are fairly large. On vehicles with metal lined heat reflective windscreens, the tag has to be placed in a "zone" near the rear view mirror which can be a distraction.
- The tags regularly become faulty, and the user cannot tell if the tag is faulty until they reach the lane. Where the reader will issue the message "Tag Error" the barrier remains closed and the lane is then blocked. At the Second Severn Crossing with a dedicated "high speed" Tag lane, this will cause a large queue to build up quickly, whilst an attendant is called to deal with the faulty tag.
- Up until January 2016, it was not possible to add funds into a Trip Tag account online, or with a credit or debit card, although it is now possible to top up a Trip Tag balance online, though Trip Tags still cannot be set to top up automatically when the account balance falls below a set threshold ("auto top-up" as is possible with e.g. the Oyster card and similar electronic tags used on the M6 Toll and Dartford Crossing).
Administration of Severn TAG
The tag is administered online, or from the Severn TAG office which is located within the Toll Administration Building at Aust. Callers may visit the office if they have problems with the Tag or wish to amend their accounts in any way. Faulty tags can also be exchanged there. Additionally a portable building is now available at the Second Severn Crossing.
- "SRC Website". Tag Introduction. Retrieved 2015-09-05.
- "Top Up Tag". Top Up Tag. Retrieved 2016-01-26.
- "Season Tag Terms and Conditions of Use" (PDF). PDF Document. Retrieved 2015-09-05.