Last month, the Congressional Research Service released a report on TRIA that gives a historical overview of the terrorism risk insurance, its legislative underpinnings, and the current usage.
"Since TRIA’s passage, the private industry’s willingness and ability to cover terrorism risk have increased. According to industry surveys, prices for terrorism coverage have generally trended downward, and approximately 60% of commercial policyholders have purchased coverage over the past few years. This relative market calm has been under the umbrella of TRIA coverage, and it is unclear how the insurance market would react to the expiration of the federal program..."
Read the CRS report.