Since　a　tunnel　is　dark　and　driving　conditions　are　monotonous,　drivers　are　prone　to　optical　illusions,　affecting　driving　safety　in　tunnels.　Tunnel　sidewall　decorations　can　provide　visual　stimulation　to　prevent　or　reduce　traffic　crashes.　Driving　simulation　experiments　with　a　driving　simulator　and　speed　perception　experiments　with　E-Prime　software　are　performed　to　evaluate　the　influence　of　tunnel　sidewall　murals　on　the　speed　control　of　drivers　in　a　long　tunnel.　Three　mural　designs　(A2:　1.93　Hz,　A3:　1.27　Hz,　A4:　0.95　Hz)　with　different　frequencies　and　a　control　group　(no　mural,　A1)　are　evaluated.　Four　indicators　of　the　driver＇s　speed　control　(speed,　acceleration,　stimulation　of　subjectively　equal　speed　(SSES),　and　reaction　time)　are　selected.　The　results　show　that　the　driver＇s　speed　is　significantly　reduced　in　the　middle　of　the　tunnel　and　near　the　tunnel　exit,　and　the　driver＇s　speed　control　is　significantly　enhanced　by　the　murals.　It　is　recommended　to　install　murals　in　the　middle　and　near　the　exit　of　the　tunnel　for　optimal　speed　control.　The　SSES　shows　that　tunnel　murals　affect　drivers＇　speed　perception　and　alertness.　As　the　frequency　of　the　mural　decreases,　speed　overestimation　changes　to　underestimation,　the　degree　of　speed　illusion　increases,　and　the　reaction　time　decreases.　A　difference　is　observed　between　the　perceived　and　actual　speed,　and　this　difference　depends　on　the　mural＇s　frequency.　Thus,　choosing　an　appropriate　mural　frequency　improves　the　mural＇s　effect.　The　results　provide　a　basis　for　mural　design　on　the　sidewalls　of　long　tunnels　to　improve　tunnel　safety,　as　well　as　a　novel　approach　for　speed　reduction.