A measure of per-mile truckload linehaul rates declined again in April along with a separate gauge of intermodal shipping costs. And there is little indication that conditions will soon improve.

The Cass Truckload Linehaul Index posted a 2.3% year-over-year drop, hitting a reading of 123, after falling 0.6% in March. Its level is the lowest since May 2015 and fell 2.2% from March.

The investment banking firm Avondale Partners, which provides analysis of the report, said these latest numbers show that risks remain to the downside of their 2016 forecasted pricing range of a 1% to a 2% gain.

They also indicated that several factors continue to contribute to excess capacity, which has helped push down rates. These include driver pay increases, overall fleet growth, reduction in carrier bankruptcies and an easing of the 34-hour restart rule.

The index is an indicator of market fluctuations in per-mile truckload pricing that isolates the linehaul component of full truckload costs from other components, such as fuel and accessorials, providing a look at trends in baseline truckload prices.

The Cass Intermodal Index continued its downward slide, falling another 3.4% year-over-year in April to a reading of 129.6, following declines of 3.8% and 3.0% in February and March, respectively.

While this latest reading is up 0.3% from the month before, following a 3.6% month-over-month gain in March, the index last posted a year-over year hike in December 2014.

Avondale Partners expects intermodal rates to continue their decline through 2016 as the dramatic drop in oil prices negatively impacts U.S. domestic demand. "We have historically observed a high degree of correlation between truckload and intermodal pricing, and know that should truckload rates accelerate in the coming months, intermodal rates would normally follow," the firm said. "That said, this is only true for the base rate, and the dramatic drop in fuel surcharges for truckers has to put pressure on domestic intermodal rates, especially in shorter lengths of haul."

The Cass Intermodal Price Index is an indicator of market fluctuations in per-mile U.S. domestic intermodal costs that includes all costs associated with the move, such as linehaul, fuel and accessorials.

It is based on costs as of January 2005 and uses a base value of 100. Data within both measures is derived from actual freight invoices paid on behalf of clients of payment processor Cass Information Systems, which totaled $25 billion in 2015.