U.S. supermarket chain Kroger said on Tuesday it has started using unmanned autonomous vehicles to deliver groceries Scottsdale, Arizona in partnership with Silicon Valley startup Nuro.

Reuters reported that the delivery service follows a pilot program started by the companies in Scottsdale in August and involved Nuro’s R1, a custom unmanned vehicle.

The driverless R1 uses public roads and is used to only transport goods.

Kroger’s deal with Nuro underscores the stiff competition in the U.S. grocery delivery market with supermarket chains angling for a bigger share of consumer spending.

Walmart and Amazon have also invested heavily in their delivery operations by expanding their offerings and shortening delivery times.

Walmart, Ford Motor Co and delivery service Postmates said last month they would collaborate to deliver groceries and other goods to Walmart customers and that could someday use autonomous vehicles.