The order will take the total number of S70s in service in Houston to 51. Siemens supplied an initial batch of 18 series H1 vehicles in 2003 and this was followed by a further tranche of 19 series H2 LRVs in 2012.

MetroRail also operates 30 series H3 vehicles supplied by CAF USA in 2015.

Siemens says the latest batch of S70s will feature an improved design with a centralised low-floor offering full low-floor access between all doors along the length of the vehicle.

Houston was the first city to opt for the S70, which entered service with the opening of the first phase of the MetroRail network in 2004. Siemens has since supplied more than 600 S70s to 11 US cities.