Enable \ Disable C# Tracing Not working - c#-4.0

Question

I created a webapi project and have used the following in the webconfig
<system.web>
<compilation debug="true" targetFramework="4.5"/>
<httpRuntime targetFramework="4.5" />
<trace enabled="false" localOnly="true" pageOutput="false" writeToDiagnosticsTrace="false"></trace>
<customErrors mode="On"/>
</system.web>
<system.diagnostics>
<trace autoflush="true">
<listeners>
<add name="TestTracer" type="System.Diagnostics.TextWriterTraceListener" initializeData="C:\Temp\Asptesttrace.log" />
</listeners>
</trace>
<sources>
<source name="Tracing" switchName="TraceSwitch">
<listeners>
<add name="TestTracer"></add>
</listeners>
</source>
</sources>
<switches>
<add name="TraceSwitch" value="0"/>
</switches>
</system.diagnostics>
My WebApiConfig.cs file has the config.EnableSystemDiagnosticsTracing(); to enable tracing
In my class file I am calling the Trace class as shown, to log the method
public void GetTipDetails()
{
System.Diagnostics.Trace.TraceInformation("Entering method - GetTipDetails");
}
Now, I want the user to enable or disable the trace using Webconfig. How do I do it?