MSBuild

aa\DispatchCar.sln

bb\DispatchCar.sln

@Set Path=C:\Windows\Microsoft.NET\Framework\v4.0.30319;%Path%
msbuild test.msbuild
pause

<?xml version="1.0" encoding="utf-8"?>
<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <ItemGroup>
    <SolutionToBuild Include=".\aa\DispatchCar.sln"><DontClean/></SolutionToBuild>
    <SolutionToBuild Include=".\bb\DispatchCar.sln"><DontClean/></SolutionToBuild>
  </ItemGroup>
  <Target Name="Build" >
    <MSBuild Projects="@(SolutionToBuild)" Targets="Build"/>
  </Target>
</Project>