Making two LinearLayouts have 50% of the screen each without using layout_weight

I'm currently doing a special xml layout of a landscape screen, where 4 images are present and 2 LinearLayouts are next to each other with 2 images each. These LinearLayouts I call linearLayout1 and linearLayout2.

linearLayout1 is marked with blue rectangle:

linearLayout2 is marked with blue rectangle:

As you can see, the first one uses ~80% of the screen, while the second one uses what's left. I don't want this of course, I want 50% for each. I can't use layout_weight because it's already used in the LinearLayouts themselves (positioning of the two images) and nested weights are bad for performance.

I've tried many different variations, but I simply can't get the two LinearLayouts to have 50% of the screen each. Here's the code:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/db1_root"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal" >

<LinearLayout
    android:id="@+id/title_container"
    style="@style/TitleBar" >

    <ImageView
        style="@style/TitleBarLogo"
        android:contentDescription="@string/imgViewDesc"
        android:src="@drawable/title_logo" />

    <ImageView
        style="@style/TitleBarSeparator"
        android:contentDescription="@string/imgViewDesc" />

    <TextView style="@style/TitleBarText" />

    <ImageButton
        style="@style/TitleBarAction"
        android:contentDescription="@string/imgViewDesc"
        android:onClick="onClickAbout"
        android:src="@drawable/title_about" />
</LinearLayout>

<RelativeLayout
    android:layout_width="fill_parent"
    android:layout_height="wra