Drivers along Interstate 680 through the San Ramon Valley may have noticed messages appearing this week on the new toll signs for the future express lanes.

The Metropolitan Transportation Commission (MTC) on Monday started testing the signage on northbound I-680 from Alcosta Boulevard to Crow Canyon Road, and if the tests prove successful, the test messages will move to other areas of the express lanes corridor through next month.

MTC officials have reminded drivers that the messages -- which include dots, toll price amounts and notifications such as "TEST 1 - NO TOLLS" or "TEST MESSAGE 2" -- are just tests and vehicles are not being tolled yet. All signs also have static "Under Construction" stickers.

The express lanes, which will run between near the Alamo-Walnut Creek border and the San Ramon-Dublin border, are now scheduled to open some time this summer, according to the MTC. When construction started in August 2015, the project was expected to open in late 2016, weather permitting.

The San Ramon Valley project aims to improve traffic congestion, but MTC officials said this month that these express lanes "are expected to improve traffic conditions in the shoulders of the peak commute hour, but likely will have only a modest impact on congestion during the heaviest travel times."

Their overarching goal is to complete two other projects aimed at creating express lanes on I-680 most of the way from Alcosta Boulevard to the Benicia-Martinez Bridge to help deliver more congestion relief throughout the freeway.

The estimated $45 million San Ramon Valley project involves converting existing high-occupancy vehicle (HOV) lanes into toll express lanes across approximately 23 miles overall. The express lanes will run on southbound I-680 from Rudgear Road to Alcosta Boulevard and on northbound I-680 from Alcosta to Livorna Road in Alamo.

The express lanes will be free to access for carpools, vanpools, public transit, motorcycles and eligible clean-air vehicles while other solo-occupant vehicles could pay a toll to use the lanes from 5 a.m. to 8 p.m. weekdays.

Motorists will need to obtain a FasTrak Flex toll tag in advance of the opening in order to use the express lanes. The FasTrak Flex reader offers adjustable settings based on one, two or three-plus vehicle occupants, allowing carpools to not be charged the toll while driving in the lanes.

The MTC this month also confirmed its plan is to create an express lane for southbound I-680 from the Benicia-Martinez Bridge to Rudgear Road by 2020, setting up a continuous express lane from the bridge to Alcosta.

The agency also plans to add a new I-680 northbound express lane from North Main Street in Walnut Creek to the bridge, although a timetable and funding sources are not yet determined. Northbound I-680 would have a gap with no express lane between North Main and Livorna, but officials said they are looking at "operational improvements," such as additional transit, to relieve bottlenecks there.