Tribal Transportation Equity and Transparency Improvement Act of 2021 This bill revises certain programs related to tribal transportation. First, the bill revises the Tribal Transportation Program (TTP) by directing the Department of the Interior to (1) request proposals from Indian tribes to include additional transportation facilities in the National Tribal Transportation Facility Inventory, and (2) ensure that all nonconfidential information from the inventory is made available on its website. Next, the bill specifies that funding allocations (i.e., tribal shares) under the TTP must be determined using the facility inventory for the most recent fiscal year for which data is available instead of using FY2012 data. It also requires each Indian tribe that intends to include a proposed road in the inventory to complete and submit certain documentation for the road. It also requires independent audits by the inspectors general of Interior and the Department of Transportation, as well as the Government Accountability Office, to review the administration of the TTP. Additionally, the bill permits Indian tribes to use funds for carrying out highway safety programs in cooperation with states, counties, and other local subdivisions. It also increases the federal share for Indian tribes under the Nationally Significant Federal Lands and Tribal Projects Program and allows Indian tribes to use planning and design funds for grant applications under the program. Finally, the bill establishes the Tribal Transportation Advisory Committee, which must provide advice to Interior and study issues related to tribal transportation.