MOT Type 3 Subbase or just Type 3 is an open graded unbound mixture of aggregates. The material grading requirements are defined in Clause 805 of the Standards for Highway Works.
Type 3 will be crushed down to a size of 80mm down to dust. It differs from MOT Type 1 because the larger sieve sizes are sued when processing the aggregates meaning the final material is much coarser.
It’s used as a subbase in construction work and can be used as an alternative to Type 1 when better drainage qualities are required.
This includes crushed rock, crushed blast furnace slag, manufactured aggregates or recycled concrete aggregate.
If used in the construction of highways then Type 3 must meet the requirements set out in Clause 805 of the Specification for Highway Works.
You can see the specifications below: